leetcode[140]Word Break II

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"].

class Solution {

public:

void dfs(string s, map<int,vector<int>> &fmap,int end, string str, vector<string> &res)

{

    if(end<0)

    {

        res.push_back(str.substr(0,str.size()-1));

        return;

    }

    for (int j=0;j<fmap[end].size();j++)

    {

        string str1=s.substr(fmap[end][j]+1,end-fmap[end][j])+" ";

        str=str1+str;

        dfs(s,fmap,fmap[end][j],str,res);

        str=str.substr(str1.size(),str.size()-str1.size());

    }

    return;

}

vector<string> wordBreak(string s, unordered_set<string> &dict) 

{

    vector<string> res;

    if(s.empty()||dict.empty())return res;

    vector<bool> dp(s.length()+1,false);

    dp[0]=true;

    map<int,vector<int>> fmap;

    for(int i=1;i<=s.length();i++)

    {

        for (int j=0;j<i;j++)

        {

            if(dp[j]&&dict.count(s.substr(j,i-j)))

            {

                dp[i]=true;

                if(j>=0)fmap[i-1].push_back(j-1);

            }

        }

    }

    string str="";

    int end=s.length()-1;

    dfs(s, fmap, end, str,res);

    return res;

}

};