word-break-ii

问题描述：

Given a string s and a dictionary of words dict, add spaces in s to construct a sentence where each word is a valid dictionary word.
Return all such possible sentences.
For example, given
s ="catsanddog",
dict =["cat", "cats", "and", "sand", "dog"].
A solution is["cats and dog", "cat sand dog"].

AC代码：

class Solution {public:    void countbreak(string &s,int index,string str,vector<int> &dp,const unordered_set<string> &dict,vector<string> &res,int &length){        string substr;        for(int len = 1; index + len <= length; ++len){            if(dp[index + len] && dict.find(s.substr(index,len)) != dict.end()){                substr = s.substr(index, len);                if(index + len >= length){                    res.push_back(str + substr);                }                else{                    countbreak(s, index + len, str + substr + " ", dp, dict, res,length);                }            }        }            }    vector<string> wordBreak(string s, unordered_set<string> &dict) {        int len=s.size();        vector<string> res;        if(len<1)            return res;        vector<int> dp(len+1,0);        dp[0]=1;        for(int i=1;i<=len;i++){            for(int j=i-1;j>=0;--j){                if(dp[j]==1 && dict.find(s.substr(j,i-j))!=dict.end())                    dp[i]=1;            }        }        if(dp[len]==0)            return res;        countbreak(s,0,"",dp,dict,res,len);        return res;    }};