Leetcode--Java--676. 实现一个魔法字典

题目描述

样例描述

思路

字典树 前缀树 trie 暴力做法

1. 构建字典树，对于每个字符，枚举修改成a~z，除了本身，看新的字符串是否在trie中存在

代码

class MagicDictionary {
    
    class TrieNode {
        TrieNode tns[] =  new TrieNode[26];
        boolean isWord;
        public TrieNode(){
           
        }
    }
    TrieNode root;
    public MagicDictionary() {
        root = new TrieNode();
    }
    
    public void buildDict(String[] dictionary) {
        for (String s: dictionary) {
            TrieNode p = root;
            for (char c: s.toCharArray()) {
                int u = c - 'a';
                if (p.tns[u] == null) {
                    p.tns[u] = new TrieNode();
                }
                p = p.tns[u];
            }
            p.isWord = true;
        }
    }
    
    public boolean search(String searchWord) {
        //先转化为字符数组，方便更改单个字母
        char ch[] = searchWord.toCharArray();
        for (int i = 0; i < ch.length; i ++ ) {
            //对于每一个词，枚举它可能替换的词a~z 除了自己本身
            for (char c = 'a'; c <= 'z'; c ++ ) {
                if (ch[i] == c) {
                    continue;
                }
                //存下原本的
                char orgi = ch[i];
                ch[i] = c;  //替换
                //判断替换后的新字符串在trie树上是否存在
                if (helper(new String(ch), root)) {
                    return true;
                }
                //记得还原，方便后续判断
                ch[i] = orgi;
            }
        }
        return false;
    }
    public boolean helper(String s, TrieNode root) {
        TrieNode p = root;
        for (char c: s.toCharArray()) {
            int u = c - 'a';
            if (p.tns[u] == null) {
                return false;
            }
            p = p.tns[u];
        }
        return p.isWord;
    }
}

/**
 * Your MagicDictionary object will be instantiated and called as such:
 * MagicDictionary obj = new MagicDictionary();
 * obj.buildDict(dictionary);
 * boolean param_2 = obj.search(searchWord);
 */