[Leetcode]Remove Invalid Parentheses

Remove the minimum number of invalid parentheses in order to make the input string valid. Return all possible results.

Note: The input string may contain letters other than the parentheses ( and).

Examples:

"()())()" -> ["()()()", "(())()"]"(a)())()" -> ["(a)()()", "(a())()"]")(" -> [""]

class Solution {public:    void dfs(string &s,vector<string>&result,string str,int l,int r,int cnt,int start){        if(l == r && l==cnt){            for(int i = start;i < s.size();i++){                if(s[i] != '(' && s[i] != ')')                    str.append(1,s[i]);            }            for(int k = 0;k < result.size();k++){                if(str == result[k])return;            }            result.push_back(str);            return;        }        for(int i = start;i < s.size();i++){            if(s[i]=='('){                if(l < cnt)dfs(s,result,str+'(',l+1,r,cnt,i+1);            }else if(s[i]==')'){                if(l > r)dfs(s,result,str+')',l,r+1,cnt,i+1);            }else{                str.append(1,s[i]);                dfs(s,result,str,l,r,cnt,i+1);            }        }    }    /*algorithm: DFS     */    vector<string> removeInvalidParentheses(string s) {        //compute minium pair count         int l = 0,r = 0;        for(int i = 0;i < s.size();i++){            if(s[i]=='(')l++;            else if(s[i]==')'&&l>r)r++;        }        vector<string>result;        dfs(s,result,"",0,0,min(l,r),0);        return result;    }};