497 lines
9.2 KiB
Go
497 lines
9.2 KiB
Go
package radix
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import (
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"sort"
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"strings"
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)
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// WalkFn is used when walking the tree. Takes a
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// key and value, returning if iteration should
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// be terminated.
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type WalkFn func(s string, v interface{}) bool
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// leafNode is used to represent a value
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type leafNode struct {
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key string
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val interface{}
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}
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// edge is used to represent an edge node
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type edge struct {
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label byte
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node *node
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}
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type node struct {
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// leaf is used to store possible leaf
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leaf *leafNode
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// prefix is the common prefix we ignore
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prefix string
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// Edges should be stored in-order for iteration.
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// We avoid a fully materialized slice to save memory,
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// since in most cases we expect to be sparse
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edges edges
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}
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func (n *node) isLeaf() bool {
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return n.leaf != nil
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}
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func (n *node) addEdge(e edge) {
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n.edges = append(n.edges, e)
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n.edges.Sort()
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}
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func (n *node) replaceEdge(e edge) {
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num := len(n.edges)
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idx := sort.Search(num, func(i int) bool {
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return n.edges[i].label >= e.label
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})
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if idx < num && n.edges[idx].label == e.label {
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n.edges[idx].node = e.node
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return
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}
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panic("replacing missing edge")
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}
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func (n *node) getEdge(label byte) *node {
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num := len(n.edges)
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idx := sort.Search(num, func(i int) bool {
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return n.edges[i].label >= label
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})
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if idx < num && n.edges[idx].label == label {
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return n.edges[idx].node
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}
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return nil
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}
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func (n *node) delEdge(label byte) {
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num := len(n.edges)
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idx := sort.Search(num, func(i int) bool {
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return n.edges[i].label >= label
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})
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if idx < num && n.edges[idx].label == label {
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copy(n.edges[idx:], n.edges[idx+1:])
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n.edges[len(n.edges)-1] = edge{}
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n.edges = n.edges[:len(n.edges)-1]
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}
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}
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type edges []edge
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func (e edges) Len() int {
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return len(e)
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}
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func (e edges) Less(i, j int) bool {
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return e[i].label < e[j].label
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}
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func (e edges) Swap(i, j int) {
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e[i], e[j] = e[j], e[i]
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}
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func (e edges) Sort() {
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sort.Sort(e)
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}
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// Tree implements a radix tree. This can be treated as a
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// Dictionary abstract data type. The main advantage over
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// a standard hash map is prefix-based lookups and
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// ordered iteration,
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type Tree struct {
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root *node
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size int
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}
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// New returns an empty Tree
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func New() *Tree {
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return NewFromMap(nil)
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}
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// NewFromMap returns a new tree containing the keys
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// from an existing map
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func NewFromMap(m map[string]interface{}) *Tree {
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t := &Tree{root: &node{}}
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for k, v := range m {
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t.Insert(k, v)
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}
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return t
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}
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// Len is used to return the number of elements in the tree
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func (t *Tree) Len() int {
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return t.size
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}
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// longestPrefix finds the length of the shared prefix
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// of two strings
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func longestPrefix(k1, k2 string) int {
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max := len(k1)
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if l := len(k2); l < max {
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max = l
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}
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var i int
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for i = 0; i < max; i++ {
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if k1[i] != k2[i] {
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break
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}
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}
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return i
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}
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// Insert is used to add a newentry or update
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// an existing entry. Returns if updated.
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func (t *Tree) Insert(s string, v interface{}) (interface{}, bool) {
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var parent *node
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n := t.root
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search := s
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for {
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// Handle key exhaution
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if len(search) == 0 {
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if n.isLeaf() {
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old := n.leaf.val
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n.leaf.val = v
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return old, true
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}
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n.leaf = &leafNode{
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key: s,
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val: v,
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}
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t.size++
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return nil, false
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}
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// Look for the edge
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parent = n
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n = n.getEdge(search[0])
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// No edge, create one
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if n == nil {
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e := edge{
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label: search[0],
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node: &node{
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leaf: &leafNode{
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key: s,
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val: v,
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},
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prefix: search,
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},
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}
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parent.addEdge(e)
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t.size++
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return nil, false
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}
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// Determine longest prefix of the search key on match
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commonPrefix := longestPrefix(search, n.prefix)
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if commonPrefix == len(n.prefix) {
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search = search[commonPrefix:]
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continue
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}
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// Split the node
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t.size++
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child := &node{
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prefix: search[:commonPrefix],
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}
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parent.replaceEdge(edge{
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label: search[0],
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node: child,
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})
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// Restore the existing node
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child.addEdge(edge{
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label: n.prefix[commonPrefix],
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node: n,
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})
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n.prefix = n.prefix[commonPrefix:]
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// Create a new leaf node
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leaf := &leafNode{
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key: s,
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val: v,
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}
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// If the new key is a subset, add to to this node
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search = search[commonPrefix:]
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if len(search) == 0 {
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child.leaf = leaf
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return nil, false
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}
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// Create a new edge for the node
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child.addEdge(edge{
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label: search[0],
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node: &node{
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leaf: leaf,
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prefix: search,
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},
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})
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return nil, false
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}
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}
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// Delete is used to delete a key, returning the previous
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// value and if it was deleted
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func (t *Tree) Delete(s string) (interface{}, bool) {
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var parent *node
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var label byte
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n := t.root
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search := s
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for {
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// Check for key exhaution
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if len(search) == 0 {
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if !n.isLeaf() {
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break
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}
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goto DELETE
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}
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// Look for an edge
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parent = n
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label = search[0]
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n = n.getEdge(label)
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if n == nil {
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break
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}
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// Consume the search prefix
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if strings.HasPrefix(search, n.prefix) {
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search = search[len(n.prefix):]
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} else {
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break
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}
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}
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return nil, false
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DELETE:
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// Delete the leaf
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leaf := n.leaf
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n.leaf = nil
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t.size--
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// Check if we should delete this node from the parent
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if parent != nil && len(n.edges) == 0 {
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parent.delEdge(label)
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}
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// Check if we should merge this node
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if n != t.root && len(n.edges) == 1 {
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n.mergeChild()
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}
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// Check if we should merge the parent's other child
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if parent != nil && parent != t.root && len(parent.edges) == 1 && !parent.isLeaf() {
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parent.mergeChild()
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}
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return leaf.val, true
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}
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func (n *node) mergeChild() {
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e := n.edges[0]
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child := e.node
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n.prefix = n.prefix + child.prefix
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n.leaf = child.leaf
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n.edges = child.edges
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}
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// Get is used to lookup a specific key, returning
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// the value and if it was found
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func (t *Tree) Get(s string) (interface{}, bool) {
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n := t.root
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search := s
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for {
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// Check for key exhaution
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if len(search) == 0 {
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if n.isLeaf() {
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return n.leaf.val, true
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}
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break
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}
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// Look for an edge
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n = n.getEdge(search[0])
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if n == nil {
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break
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}
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// Consume the search prefix
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if strings.HasPrefix(search, n.prefix) {
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search = search[len(n.prefix):]
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} else {
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break
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}
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}
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return nil, false
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}
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// LongestPrefix is like Get, but instead of an
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// exact match, it will return the longest prefix match.
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func (t *Tree) LongestPrefix(s string) (string, interface{}, bool) {
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var last *leafNode
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n := t.root
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search := s
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for {
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// Look for a leaf node
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if n.isLeaf() {
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last = n.leaf
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}
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// Check for key exhaution
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if len(search) == 0 {
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break
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}
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// Look for an edge
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n = n.getEdge(search[0])
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if n == nil {
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break
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}
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// Consume the search prefix
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if strings.HasPrefix(search, n.prefix) {
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search = search[len(n.prefix):]
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} else {
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break
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}
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}
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if last != nil {
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return last.key, last.val, true
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}
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return "", nil, false
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}
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// Minimum is used to return the minimum value in the tree
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func (t *Tree) Minimum() (string, interface{}, bool) {
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n := t.root
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for {
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if n.isLeaf() {
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return n.leaf.key, n.leaf.val, true
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}
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if len(n.edges) > 0 {
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n = n.edges[0].node
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} else {
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break
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}
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}
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return "", nil, false
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}
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// Maximum is used to return the maximum value in the tree
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func (t *Tree) Maximum() (string, interface{}, bool) {
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n := t.root
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for {
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if num := len(n.edges); num > 0 {
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n = n.edges[num-1].node
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continue
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}
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if n.isLeaf() {
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return n.leaf.key, n.leaf.val, true
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}
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break
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}
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return "", nil, false
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}
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// Walk is used to walk the tree
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func (t *Tree) Walk(fn WalkFn) {
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recursiveWalk(t.root, fn)
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}
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// WalkPrefix is used to walk the tree under a prefix
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func (t *Tree) WalkPrefix(prefix string, fn WalkFn) {
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n := t.root
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search := prefix
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for {
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// Check for key exhaution
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if len(search) == 0 {
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recursiveWalk(n, fn)
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return
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}
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// Look for an edge
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n = n.getEdge(search[0])
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if n == nil {
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break
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}
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// Consume the search prefix
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if strings.HasPrefix(search, n.prefix) {
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search = search[len(n.prefix):]
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} else if strings.HasPrefix(n.prefix, search) {
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// Child may be under our search prefix
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recursiveWalk(n, fn)
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return
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} else {
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break
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}
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}
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}
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// WalkPath is used to walk the tree, but only visiting nodes
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// from the root down to a given leaf. Where WalkPrefix walks
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// all the entries *under* the given prefix, this walks the
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// entries *above* the given prefix.
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func (t *Tree) WalkPath(path string, fn WalkFn) {
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n := t.root
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search := path
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for {
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// Visit the leaf values if any
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if n.leaf != nil && fn(n.leaf.key, n.leaf.val) {
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return
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}
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// Check for key exhaution
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if len(search) == 0 {
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return
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}
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// Look for an edge
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n = n.getEdge(search[0])
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if n == nil {
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return
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}
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// Consume the search prefix
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if strings.HasPrefix(search, n.prefix) {
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search = search[len(n.prefix):]
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} else {
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break
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}
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}
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}
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// recursiveWalk is used to do a pre-order walk of a node
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// recursively. Returns true if the walk should be aborted
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func recursiveWalk(n *node, fn WalkFn) bool {
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// Visit the leaf values if any
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if n.leaf != nil && fn(n.leaf.key, n.leaf.val) {
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return true
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}
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// Recurse on the children
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for _, e := range n.edges {
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if recursiveWalk(e.node, fn) {
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return true
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}
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}
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return false
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}
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// ToMap is used to walk the tree and convert it into a map
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func (t *Tree) ToMap() map[string]interface{} {
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out := make(map[string]interface{}, t.size)
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t.Walk(func(k string, v interface{}) bool {
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out[k] = v
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return false
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})
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return out
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}
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