LeetCode-Longest Valid Parentheses

Given a string containing just the characters '(' and ')', find the length of the longest valid (well-formed) parentheses substring.

For "(()", the longest valid parentheses substring is "()", which has length = 2.

Another example is ")()())", where the longest valid parentheses substring is "()()", which has length = 4.

class Solution {
public:
    int longestValidParentheses(string s) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        stack<int> left;
        int max=0;
        vector<bool> vec;
        vec.resize(s.length(),false);
        for(int i=0;i<s.length();i++){
            if(s[i]=='(')left.push(i);
            else if(s[i]==')'){
                if(left.size()!=0)
                {
                    vec[left.top()]=true;
                    left.pop();
                    vec[i]=true;
                }
            }
        }
        int count=0;
        for(int i=0;i<s.length();i++){
            if(vec[i]){
                
                count++;
                if(count>max)max=count;
            }
            else count=0;
        }
        return max;
    }
};