leetcode——20——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) {
        stack<char> stk;
       
        for(int i = 0; i<s.length();i++)
        {
            if(s[i]=='('||s[i]=='{'||s[i]=='[')
               stk.push(s[i]);
            else {
                if (stk.empty())
                    return false;
                char tmp = stk.top(); 
                if(s[i]==')'||s[i]=='}'||s[i]==']')
                {
                   
                   if( (tmp=='('&&s[i]==')') || (tmp=='['&&s[i]==']') || (tmp=='{'&&s[i]=='}') ) 
                        stk.pop();  
                   else return false;
                   
                  
                   
                }
            }    
        }
        if (stk.empty())
               return true;
        else  return false;
    }
};