go: add «208. Implement Trie (Prefix Tree)»

Signed-off-by: Matej Focko <me@mfocko.xyz>

go/implement-trie-prefix-tree.go

@@ -0,0 +1,85 @@
+package implement_trie_prefix_tree
+
+type TrieNode struct {
+	has        bool
+	successors [26]*TrieNode
+}
+
+type Trie struct {
+	root TrieNode
+}
+
+func Constructor() Trie {
+	return Trie{}
+}
+
+func (this *Trie) Insert(word string) {
+	node := &this.root
+
+	for _, c := range word {
+		idx := int(c) - int('a')
+
+		if node.successors[idx] == nil {
+			node.successors[idx] = new(TrieNode)
+		}
+		node = node.successors[idx]
+	}
+
+	node.has = true
+}
+
+func (this *Trie) findPrefix(prefix string) *TrieNode {
+	node := &this.root
+
+	for _, c := range prefix {
+		idx := int(c) - int('a')
+
+		if node.successors[idx] == nil {
+			return nil
+		}
+		node = node.successors[idx]
+	}
+
+	return node
+}
+
+func (this *Trie) Search(word string) bool {
+	node := this.findPrefix(word)
+	return node != nil && node.has
+}
+
+func (this *Trie) StartsWith(prefix string) bool {
+	var terminates func(*TrieNode) bool
+	terminates = func(node *TrieNode) bool {
+		if node == nil {
+			return false
+		}
+
+		if node.has {
+			return true
+		}
+
+		for _, succ := range node.successors {
+			if terminates(succ) {
+				return true
+			}
+		}
+
+		return false
+	}
+
+	node := this.findPrefix(prefix)
+	if node == nil {
+		return false
+	}
+
+	return terminates(node)
+}
+
+/**
+ * Your Trie object will be instantiated and called as such:
+ * obj := Constructor();
+ * obj.Insert(word);
+ * param_2 := obj.Search(word);
+ * param_3 := obj.StartsWith(prefix);
+ */