Trie - 208. Implement Trie (Prefix Tree)

208. Implement Trie (Prefix Tree)

Implement a trie with insert, search, and startsWith methods.

Example:

Trie trie = new Trie();

trie.insert("apple");
trie.search("apple");   // returns true
trie.search("app");     // returns false
trie.startsWith("app"); // returns true
trie.insert("app");   
trie.search("app");     // returns true

Note:

• You may assume that all inputs are consist of lowercase letters a-z.
• All inputs are guaranteed to be non-empty strings.

思路：

题目意思很明确，就是实现一下前缀树的几个api，前缀树有用在路由匹配等场景，具体思路都差不多，实现出来之后，可以有很多优化的点，比如插入前缀一个单词等。这里写一下最基本的一个写法，这里使用数组，没有用map来存节点的子节点。

代码：

go：

type Trie struct {

	IsWord bool
	Children [26]*Trie
}


/** Initialize your data structure here. */
func Constructor() Trie {
	return Trie{
		IsWord  : false,
		Children: [26]*Trie{},
	}
}


/** Inserts a word into the trie. */
func (this *Trie) Insert(word string)  {
	cur := this
    for i:=0; i<len(word); i++ {
        c := rune(word[i])
		if cur.Children[c - 'a'] == nil {
			newNode := Constructor()
			cur.Children[c - 'a'] = &newNode
	}
		cur = cur.Children[c - 'a']
	}
	cur.IsWord = true
}


/** Returns if the word is in the trie. */
func (this *Trie) Search(word string) bool {
	cur := this
    for i:=0; i<len(word); i++ {
        c := rune(word[i])
		if cur.Children[c - 'a'] == nil {
			return false
		}
		cur = cur.Children[c - 'a']
	}
	return cur.IsWord
}


/** Returns if there is any word in the trie that starts with the given prefix. */
func (this *Trie) StartsWith(prefix string) bool {
	cur := this
    for i := 0; i < len(prefix); i++ {
        c := rune(prefix[i])
		if cur.Children[c - 'a'] == nil {
			return false
		}
		cur = cur.Children[c - 'a']
	}
	return true
}


/**
 * 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);
 */