Implement Trie (Prefix Tree) ——LeetCode

Implement a trie with

insert

,

search

, and

startsWith

methods.

Note:
You may assume that all inputs are consist of lowercase letters

a-z

.

实现一个字典树。

好久不做题，没感觉啊，TreeNode用一个布尔变量表示是否是一个合法单词的结尾即可，一开始还用cnt来计数，search的时候比较麻烦。

class TrieNode {
// Initialize your data structure here.
TrieNode [] next;
boolean valid;
public TrieNode() {
next = new TrieNode[26];
valid=false;
}
}

public class Trie {
private TrieNode root;

public Trie() {
root = new TrieNode();
}

// Inserts a word into the trie.
public void insert(String word) {
TrieNode ptr = root;
for(char c:word.toCharArray()){
if(ptr.next[c-'a']==null){
ptr.next[c-'a'] = new TrieNode();
}
ptr=ptr.next[c-'a'];
}
ptr.valid=true;
}

// Returns if the word is in the trie.
public boolean search(String word) {
int last = 0;
TrieNode ptr = root;
for(char c:word.toCharArray()){
if(ptr==null||ptr.next[c-'a']==null){
return false;
}
ptr=ptr.next[c-'a'];
}
return ptr.valid;
}

// Returns if there is any word in the trie
// that starts with the given prefix.
public boolean startsWith(String prefix) {
TrieNode ptr = root;
for(char c:prefix.toCharArray()){
if(ptr==null||ptr.next[c-'a']==null){
return false;
}
ptr=ptr.next[c-'a'];
}
return true;
}
}

// Your Trie object will be instantiated and called as such:
// Trie trie = new Trie();
// trie.insert("somestring");
// trie.search("key");