LeetCode _ Word Break

Given a string s and a dictionary of words dict, determine if s can be segmented into a space-separated sequence of one or more dictionary words.

For example, given
s = "leetcode",
dict = ["leet", "code"].

Return true because "leetcode" can be segmented as "leet code".

　　DP 

class Solution {
public:
    bool wordBreak(string s, unordered_set<string> &dict) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        int len = s.size();
        if(len <1) return false;
        if(dict.size() == 0) return false;
        vector<bool> flag(len+1,false);
        flag[0] = true;
        for(int i = 1; i< len+1;++i){
            for(int j = i-1; j>=0;--j)
                if(flag[j]==true && dict.find(s.substr(j,i-j))!= dict.end())
                {
                    flag[i] = true;
                    break;
                }
        }
        return flag[len];
    }
};