I tried to solve 20. ‘Valid Parentheses’.

Problem

20. Valid Parentheses

problem

My idea

I use stack. next char should correspond last char.

Correct Solution

class Solution {
public:
       
    bool isValid(string ss) {
        map<char,char> cor{
            {'(',')'},
            {'{','}'},
            {'[',']'}
        };
        vector<char> stack;
        for(const auto& s : ss){
            if(s == '(' || s == '[' || s == '{'){
                stack.push_back(s);
            }else if(s == ')' || s == ']' || s == '}'){
                if(stack.empty()){ return false; }
                if(cor[stack.back()] != s){
                    return false;
                }
                stack.pop_back();
            }
        }
        return stack.empty();
    }
};

My wrong idea

In first, I think sum of ‘(’,’[‘,’{’ equals sum of ‘)’,‘]’,‘}’.
but this test case is failed.

Input: "([)]"  
Output: true  
Expected: false  

bool isValid(string ss) {
    auto mn = 0;
    auto sn = 0;
    auto nn = 0;
    
    for(const auto& s : ss){
        if(s == '('){
            mn++;
        }else if(s == '['){
            sn++;
        }else if(s == '{'){
            nn++;
        }else if(s == ')'){
            if(mn == 0){ return false; }
            mn--;
        }else if(s == ']'){
            if(sn == 0){ return false; }
            sn--;
        }else if(s == '}'){
            if(nn == 0){ return false; }
            nn--;
        }
    }
    return (mn == 0 && sn == 0 && nn == 0);
}