【Lintcode】1221. Concatenated Words

题目地址：

https://www.lintcode.com/problem/concatenated-words/description

给定一个非空英文小写字符串组成的数组$A$，题目保证字符串两两不同，返回其所有能被至少两个别的字符串拼接而成的字符串。同一个字符串可以被多次使用。

参考https://blog.csdn.net/qq_46105170/article/details/112428099。代码如下：

import java.util.*;

public class Solution {
    
    
    /**
     * @param words: List[str]
     * @return: return List[str]
     */
    public List<String> findAllConcatenatedWordsInADict(String[] words) {
    
    
        // write your code here
        List<String> res = new ArrayList<>();
        Set<String> set = new HashSet<>();
        
        Arrays.sort(words, (w1, w2) -> Integer.compare(w1.length(), w2.length()));
        for (int i = 0; i < words.length; i++) {
    
    
            if (check(words[i], set)) {
    
    
                res.add(words[i]);
            }
            
            set.add(words[i]);
        }
        
        return res;
    }
    
    private boolean check(String s, Set<String> set) {
    
    
        int[] dp = new int[s.length() + 1];
        Arrays.fill(dp, -1);
        dp[0] = 0;
        
        for (int i = 0; i < s.length(); i++) {
    
    
            if (dp[i] == -1) {
    
    
                continue;
            }
            
            for (int j = s.length() - i; j >= 0; j--) {
    
    
                if (set.contains(s.substring(i, i + j))) {
    
    
                    dp[i + j] = Math.max(dp[i + j], dp[i] + 1);
                }
                
                if (dp[s.length()] > 1) {
    
    
                    return true;
                }
            }
        }
        
        return false;
    }
}

时间复杂度$O(nl\log n+n{l}^3)$，$l$是最长字符串长度，空间$O(nl)$。