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:

 1   bool wordBreak(string s, unordered_set<string>& wordDict) {

 2         //flag[i][j]表示s[i]...s[j]是否为一个word

 3       int length = s.size();  

 4      bool flag[MAX][MAX]={false};

 5       for (int i = 0; i < length; ++i)

 6       {

 7         string str(s,i,1);

 8         if (wordDict.find(str)!=wordDict.end())

 9             flag[i][i] = true;

10       }

11      

12      for (int r=2; r<=length; ++r)

13      {//计算长度为2,3，...n的字符串

14          for (int i=0; i <= length-r; ++i)

15          {

16              int j = i+r-1;//j<=length-1

17             //计算flag[i][j];

18             string str(s,i,r);

19             if (wordDict.find(str)!=wordDict.end())

20             {

21                 flag[i][j] = true;

22                 continue;

23             }

24              for (int k = i; k < j; ++k)

25              {

26                  if (flag[i][k]&&flag[k+1][j])

27                  {

28                     flag[i][j] = true;

29                     break;

30                  }

31              }

32          }

33      }

34       return flag[0][length-1];

35     }