LeetCode-Valid Parentheses

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not.

class Solution {
public:
    bool isValid(string s) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int l1=0,l2=0,l3=0;
        for(int i=0;i<s.length();i++){
            if(s[i]=='(')l1++;
            else if(s[i]=='[')l2++;
            else if(s[i]=='{')l3++;
            else{
                if(s[i]==')'){
                    if(l1==0)return false;
                    else l1--;
                    if(s[i-1]=='['||s[i-1]=='{')return false;
                }
                else if(s[i]==']'){
                    if(l2==0)return false;
                    else l2--;
                     if(s[i-1]=='('||s[i-1]=='{')return false;
                }
                else if(s[i]=='}'){
                    if(l3==0)return false;
                    else l3--;
                     if(s[i-1]=='['||s[i-1]=='(')return false;
                }
            }
        }
        if(l1>0||l2>0||l3>0)return false;
        return true;
    }
};