Valid_parentheses

/*
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> mystack;
      if (s.size()==0) return true;
      for (int i=0; i<s.size(); ++i)
      {
        
	if(!mystack.empty()&&s[i]==')'&&mystack.top()=='(')
	{
	  mystack.pop();
	}
	else if(!mystack.empty()&&s[i]==']'&&mystack.top()=='[')
	{
	  mystack.pop();
	}
	else if(!mystack.empty()&&s[i]=='}'&&mystack.top()=='{')
	{
	  mystack.pop();
	}
	else mystack.push(s[i]);
      }
      return mystack.empty(); 
    }
};

REMARK:
1.IDEA:
Use a stack.
If stack is not empty && top of the stack matches the next char in the string, we pop the top element in the stack
Else: push the next char into the stack.
Finally, after loop through all the char in the string, return true if the stack is empty or return false if the stack is not empty.