leetcode(word break)

题目要求：

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".

代码：

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