139. 单词拆分

class Solution {
public:bool wordBreak(string s, vector<string>& wordDict) {vector<bool> dp(s.size()+1, false);unordered_set<string> wordDict_set;for (int i=0; i<wordDict.size(); i++){wordDict_set.insert(wordDict[i]);}dp[0] = true;for (int i=1; i<dp.size();i++){for (int m=i-1; m>=0; m--){if (!dp[i] && dp[m]){if (wordDict_set.count(s.substr(m, i-m))) {dp[i]=true;break;}}}}return dp[s.size()];}
};