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103 lines
2.4 KiB
103 lines
2.4 KiB
// Package trie is an implementation of a trie (prefix tree) data structure over byte slices. It provides a
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// small and simple API for usage as a set as well as a 'Node' API for walking the trie.
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package trie
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// A Trie is a a prefix tree.
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type Trie struct {
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root *Node
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}
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// New construct a new, empty Trie ready for use.
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func New() *Trie {
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return &Trie{
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root: &Node{},
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}
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}
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// Insert puts b into the Trie. It returns true if the element was not previously in t.
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func (t *Trie) Insert(b []byte) bool {
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n := t.root
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for _, c := range b {
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next, ok := n.Walk(c)
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if !ok {
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next = &Node{}
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n.branches[c] = next
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n.hasChildren = true
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}
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n = next
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}
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if n.terminal {
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return false
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}
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n.terminal = true
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return true
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}
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// Contains checks t for membership of b.
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func (t *Trie) Contains(b []byte) bool {
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n := t.root
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for _, c := range b {
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next, ok := n.Walk(c)
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if !ok {
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return false
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}
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n = next
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}
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return n.terminal
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}
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// PrefixIndex walks through `b` until a prefix is found (terminal node) or it is exhausted.
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func (t *Trie) PrefixIndex(b []byte) int {
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var idx int
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n := t.root
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for _, c := range b {
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next, ok := n.Walk(c)
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if !ok {
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return -1
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}
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if next.terminal {
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return idx
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}
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n = next
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idx++
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}
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if !n.terminal {
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idx = -1
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}
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return idx
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}
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// Root returns the root node of a Trie. A valid Trie (i.e., constructed with New), always has a non-nil root
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// node.
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func (t *Trie) Root() *Node {
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return t.root
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}
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// A Node represents a logical vertex in the trie structure.
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type Node struct {
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branches [256]*Node
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terminal bool
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hasChildren bool
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}
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// Walk returns the node reached along edge c, if one exists. The ok value indicates whether such a node
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// exist.
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func (n *Node) Walk(c byte) (next *Node, ok bool) {
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next = n.branches[int(c)]
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return next, (next != nil)
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}
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// Terminal indicates whether n is terminal in the trie (that is, whether the path from the root to n
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// represents an element in the set). For instance, if the root node is terminal, then []byte{} is in the
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// trie.
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func (n *Node) Terminal() bool {
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return n.terminal
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}
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// Leaf indicates whether n is a leaf node in the trie (that is, whether it has children). A leaf node must be
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// terminal (else it would not exist). Logically, if n is a leaf node then the []byte represented by the path
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// from the root to n is not a proper prefix of any element of the trie.
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func (n *Node) Leaf() bool {
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return !n.hasChildren
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}
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