Word Break

Description:

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".

Code:

  bool wordBreak(string s, unordered_set<string>& wordDict) {
        //flag[i][j]表示s[i]...s[j]是否为一个word
      int length = s.size();  
     bool flag[MAX][MAX]={false};
      for (int i = 0; i < length; ++i)
      {
        string str(s,i,1);
        if (wordDict.find(str)!=wordDict.end())
            flag[i][i] = true;
      }
     
     for (int r=2; r<=length; ++r)
     {//计算长度为2,3，...n的字符串
         for (int i=0; i <= length-r; ++i)
         {
             int j = i+r-1;//j<=length-1
            //计算flag[i][j];
            string str(s,i,r);
            if (wordDict.find(str)!=wordDict.end())
            {
                flag[i][j] = true;
                continue;
            }
             for (int k = i; k < j; ++k)
             {
                 if (flag[i][k]&&flag[k+1][j])
                 {
                    flag[i][j] = true;
                    break;
                 }
             }
         }
     }
      return flag[0][length-1];
    }