131 Palindrome Partitioning 分割回文串

class Solution {
public:
    vector<vector<string>> partition(string s) {
        vector<vector<string>> res;
        vector<string> out;
        if(s.size()==0||s.empty())
        {
            return res;
        }
        helper(s,0,out,res);
        return res;
    }
    void helper(string &s,int start,vector<string> &out,vector<vector<string>> &res)
    {
        if(start==s.size())
        {
            res.push_back(out);
            return;
        }
        for(int i=start;i<s.size();++i)
        {
            if(isPalindrome(s,start,i))
            {
                out.push_back(s.substr(start,i-start+1));
                helper(s,i+1,out,res);
                out.pop_back();
            }
        }
    }
    bool isPalindrome(string &s,int start,int end)
    {
        while(start<end)
        {
            if(s[start]!=s[end])
            {
                return false;
            }
            ++start;
            --end;
        }
        return true;
    }
};