题解 | #训练聪明的牛#

import java.util.*;

public class Solution {
    //依旧是最常规的递归，动态规划可自行尝试修改
    HashMap<Character, Integer> map = new HashMap<>();
    StringBuilder sb = new StringBuilder();
    String[] st;
    public boolean wordBreak (String s, String[] wordDict) {
        sb.append(s);
        st = wordDict;
        for (int i = 0; i < wordDict.length; i++) {
            map.put(wordDict[i].charAt(0), i);
        }
        return dfs();
    }
    public boolean dfs() {
        if (sb.length() == 0) {
            return true;
        }
        if (!map.containsKey(sb.charAt(0))) return false;
        int index = map.get(sb.charAt(0));
        int len = st[index].length();
        if (sb.length() < len) return false;
        for (int i = 0; i < len; i++) {
            if (sb.charAt(0) == st[index].charAt(i)) {
                sb.deleteCharAt(0);
            } else {
                return false;
            }
        }
        return dfs();
    }
}