题目描述

• 属于那种，敲过一遍就不会忘了的那种题，就是学一个新的数据结构= =
• 二十六叉树！
  

思路 & 代码

• isEnd 非常重要噢，只有正式 insert 了的单词才能被 search 到。
• 在 Trie 中实现内部类 TrieNode
• 说实话，insert、search、startWith 三个函数的结构都十分相似= =
• 注意 new Node 的时候小心。。引用丢失就难受了

class Trie {private class TrieNode{boolean isEnd;TrieNode[] next;TrieNode(){isEnd = false;next = new TrieNode[26];}}private TrieNode root;/** Initialize your data structure here. */public Trie() {root = new TrieNode();}/** Inserts a word into the trie. */// 没则插，结尾改 true （出现了，但是没真正 insert 的话，不算：比如 insert apple , 然后 search app = falsepublic void insert(String word) {char[] wordC = word.toCharArray();TrieNode nowNode = root;for(int i = 0; i < wordC.length; i++){// error：TrieNode nextNode = nowNode.next[wordC[i] - 'a']; nextNode = new TrieNode()// 会直接丢失引用！int index = wordC[i] - 'a';if(nowNode.next[index] == null){nowNode.next[index] = new TrieNode();}nowNode = nowNode.next[index];}// 结束，标志单词结尾字符nowNode.isEnd = true;}/** Returns if the word is in the trie. */public boolean search(String word) {char[] wordC = word.toCharArray();TrieNode nowNode = root;for(int i = 0; i < wordC.length; i++){int index = wordC[i] - 'a';if(nowNode.next[index] == null){return false;}nowNode = nowNode.next[index];}return nowNode.isEnd;}/** Returns if there is any word in the trie that starts with the given prefix. */public boolean startsWith(String prefix) {char[] wordC = prefix.toCharArray();TrieNode nowNode = root;for(int i = 0; i < wordC.length; i++){int index = wordC[i] - 'a';if(nowNode.next[index] == null){return false;}nowNode = nowNode.next[index];}return true;}
}/*** Your Trie object will be instantiated and called as such:* Trie obj = new Trie();* obj.insert(word);* boolean param_2 = obj.search(word);* boolean param_3 = obj.startsWith(prefix);*/

更新版

• 其实三个函数的代码都差不多= =
• 前缀树：存储字符串的一种树结构（二十六叉树），可以实现拼写检查、自动补全功能。

class Trie {TrieNode root;private class TrieNode {boolean isEnd;TrieNode[] nextNode;public TrieNode() {isEnd = false;nextNode = new TrieNode[26];}}public Trie() {root = new TrieNode();}public void insert(String word) {TrieNode nowNode = root;for(char c : word.toCharArray()) {int index = c - 'a';if(nowNode.nextNode[index] == null) {nowNode.nextNode[index] = new TrieNode();}nowNode = nowNode.nextNode[index];}nowNode.isEnd = true;}public boolean search(String word) {TrieNode nowNode = root;for(char c : word.toCharArray()) {int index = c - 'a';if(nowNode.nextNode[index] == null) {return false;}nowNode = nowNode.nextNode[index];}return nowNode.isEnd;}public boolean startsWith(String prefix) {TrieNode nowNode = root;for(char c : prefix.toCharArray()) {int index = c - 'a';if(nowNode.nextNode[index] == null) {return false;}nowNode = nowNode.nextNode[index];}return true;}
}