LeetCode 刷题【139. 单词拆分】

139. 单词拆分

自己做（超时）

class Solution {
    private boolean is_exist = false;

    public void searchWord(String s, int begin, List<String> wordDict){
        if(begin == s.length()){
            is_exist = true;
            return;
        }

        for(int i = 0; i < wordDict.size(); i++)
            for(int j = begin; j < s.length() && j - begin + 1 <= wordDict.get(i).length(); j++)
                if(s.substring(begin, j + 1).equals(wordDict.get(i)))
                    searchWord(s, j + 1, wordDict);

    }


    public boolean wordBreak(String s, List<String> wordDict) {
        searchWord(s, 0, wordDict);

        return is_exist;
    }
}

看题解

官方题解

public class Solution {
    public boolean wordBreak(String s, List<String> wordDict) {
        Set<String> wordDictSet = new HashSet(wordDict);
        boolean[] dp = new boolean[s.length() + 1];
        dp[0] = true;
        for (int i = 1; i <= s.length(); i++) {
            for (int j = 0; j < i; j++) {
                if (dp[j] && wordDictSet.contains(s.substring(j, i))) {
                    dp[i] = true;
                    break;
                }
            }
        }
        return dp[s.length()];
    }
}