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) {
		bool f = true;
		while (!s.empty()&&f)
		{ 
		    f=false;
			int i = 0;
			while (!s.empty() && i < s.length() - 1)
			{
				if (s[i] == '('&&s[i + 1] == ')' || s[i] == '['&&s[i + 1] == ']'
					|| s[i] == '{'&&s[i + 1] == '}')
				{
					f = true;
					s.erase(i, 2);
				}
				else
					i++;
			}
		}
		return s.empty();
	}
};

accepted