Implement Trie (Prefix Tree)
Implement a trie with insert
, search
, and startsWith
methods.
Note:
You may assume that all inputs are consist of lowercase letters a-z
.
由于用的是 26位字母的array, 所以在trieNode 上甚至不用存val。
1 class TrieNode { 2 // Initialize your data structure here. 3 Boolean isWord; 4 TrieNode[] children; 5 6 public TrieNode(){ 7 this.isWord = false; 8 children = new TrieNode[26]; 9 } 10 } 11 12 public class Trie { 13 private TrieNode root; 14 15 public Trie() { 16 root = new TrieNode(); 17 } 18 19 // Inserts a word into the trie. 20 public void insert(String word) { 21 TrieNode cur = root; 22 for(int i = 0; i < word.length(); i ++){ 23 Character c = word.charAt(i); 24 if(cur.children[c - 'a'] == null){ 25 TrieNode tmp = new TrieNode(); 26 cur.children[c - 'a'] = tmp; 27 } 28 cur = cur.children[c - 'a']; 29 } 30 cur.isWord = true; 31 } 32 33 private TrieNode findNode(String word){ 34 TrieNode cur = root; 35 for(int i = 0; i < word.length(); i ++){ 36 Character c = word.charAt(i); 37 if(cur.children[c - 'a'] == null){ 38 return null; 39 } 40 cur = cur.children[c - 'a']; 41 } 42 return cur; 43 } 44 45 // Returns if the word is in the trie. 46 public boolean search(String word) { 47 TrieNode end = findNode(word); 48 return end != null && end.isWord; 49 } 50 51 // Returns if there is any word in the trie 52 // that starts with the given prefix. 53 public boolean startsWith(String prefix) { 54 return findNode(prefix) != null; 55 } 56 } 57 58 // Your Trie object will be instantiated and called as such: 59 // Trie trie = new Trie(); 60 // trie.insert("somestring"); 61 // trie.search("key");
posted on 2015-05-08 12:44 Step-BY-Step 阅读(210) 评论(0) 编辑 收藏 举报