Note:

• The same word in the dictionary may be reused multiple times in the segmentation.
• You may assume the dictionary does not contain duplicate words.

Example 1:

Input: s = "leetcode", wordDict = ["leet", "code"]

Output: true

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

Example 2:

Input: s = "applepenapple", wordDict = ["apple", "pen"]

Output: true

Explanation: Return true because "applepenapple" can be segmented as "apple pen apple".

             Note that you are allowed to reuse a dictionary word.

Example 3:

Input: s = "catsandog", wordDict = ["cats", "dog", "sand", "and", "cat"]

Output: false

dp[i]  0-i这个字符串是否满足wordbreak

dp[0] = 0

dp[1] =dp[0] && s[0:1] in dict

dp[2] =dp[0] && s[0:1] in dict  ||  dp[1] && s[1:2] in dict

dp[3] =dp[0] && s[0:3] in dict  ||  dp[1] && s[1:3] in dict ||  dp[2] && s[2:3] in dict

dp[i] =dp[0] && s[0:i] in dict || ,,,,,,,||dp[i-1]&& s[i-1:i] in dict

Time complexity O(n^2)

Space complexity O(n)

语法注意：

s = "abcde"; 要得到”ce“

string word = s.substr(2,2);

 class Solution {

 public:

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

         vector<bool> dp(s.size()+,false);

         unordered_set<string>dict(wordDict.begin(),wordDict.end());

         dp[] = true;

         for(int i =  ; i<=s.size();i++){

             for(int j = ;j<i;j++){

                 string word = s.substr(j,i-j);

                 if(dp[j]&&dict.find(word)!=dict.end()){

                     cout<<word<<endl;

                     dp[i] = true;

                     break;

                 }

             }

         }

         return dp[s.size()];

     }

 };

参考：
http://zxi.mytechroad.com/blog/leetcode/leetcode-139-word-break/