Note:
You may assume that all inputs are consist of lowercase letters a-z.
设计一个字典树(前缀树),题目中假设字典中包含的字母为a-z, 我们可以设定树中每个节点都有两个属性,一个为TrieNode[], 另一个为一个布尔变量isLast。TrieNode[] 用来存放insert操作时对应的字符,isLast对应search操作是是否包含这个元素。代码如下:
class TrieNode { boolean isLast; TrieNode[] trieNode; // Initialize your data structure here. public TrieNode() { isLast = false; trieNode = new TrieNode[26]; } } public class Trie { private TrieNode root; public Trie() { root = new TrieNode(); } // Inserts a word into the trie. public void insert(String word) { TrieNode cur = root; for(char c : word.toCharArray()) { if(cur.trieNode[c - 'a'] == null) { cur.trieNode[c - 'a'] = new TrieNode(); } cur = cur.trieNode[c - 'a']; } cur.isLast = true; } // Returns if the word is in the trie. public boolean search(String word) { TrieNode cur = root; for(char c : word.toCharArray()) { if(cur.trieNode[c - 'a'] == null) return false; cur = cur.trieNode[c - 'a']; } return cur.isLast; } // Returns if there is any word in the trie // that starts with the given prefix. public boolean startsWith(String prefix) { TrieNode cur = root; for(char c : prefix.toCharArray()) { if(cur.trieNode[c - 'a'] == null) return false; cur = cur.trieNode[c - 'a']; } return true; } } // Your Trie object will be instantiated and called as such: // Trie trie = new Trie(); // trie.insert("somestring"); // trie.search("key");