# [208. Implement Trie (Prefix Tree)](https://leetcode.com/problems/implement-trie-prefix-tree/)


## 题目

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.

## 题目大意

实现一个 Trie (前缀树)，包含 insert, search, 和 startsWith 这三个操作。

## 解题思路

- 要求实现一个 Trie 的数据结构，具有 `insert`, `search`, `startsWith` 三种操作
- 这一题就是经典的 Trie 实现。本题的实现可以作为 Trie 的模板。


## 代码

```go

package leetcode

type Trie struct {
	isWord   bool
	children map[rune]*Trie
}

/** Initialize your data structure here. */
func Constructor208() Trie {
	return Trie{isWord: false, children: make(map[rune]*Trie)}
}

/** Inserts a word into the trie. */
func (this *Trie) Insert(word string) {
	parent := this
	for _, ch := range word {
		if child, ok := parent.children[ch]; ok {
			parent = child
		} else {
			newChild := &Trie{children: make(map[rune]*Trie)}
			parent.children[ch] = newChild
			parent = newChild
		}
	}
	parent.isWord = true
}

/** Returns if the word is in the trie. */
func (this *Trie) Search(word string) bool {
	parent := this
	for _, ch := range word {
		if child, ok := parent.children[ch]; ok {
			parent = child
			continue
		}
		return false
	}
	return parent.isWord
}

/** Returns if there is any word in the trie that starts with the given prefix. */
func (this *Trie) StartsWith(prefix string) bool {
	parent := this
	for _, ch := range prefix {
		if child, ok := parent.children[ch]; ok {
			parent = child
			continue
		}
		return false
	}
	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);
 */

```