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.

题目要求判断括号是否匹配，可以通过栈来实现。

代码如下：

class Solution {
public:
              bool isValid(string s) {
        		stack<char> opstack;
			char c ;
			for (int i=0; i<s.size(); i++)
			{
				c = s[i];
				if ((c=='(') || (c=='[') || (c=='{'))
				{
					opstack.push(c);
				}
				else if ((c==')') || (c==']') || (c=='}'))
				{
				    if (opstack.empty())
					{
						return false;
					}
					char tmp = opstack.top();
				if ((c==')' && tmp=='(') || (tmp=='[' &&c==']' ) ||(tmp=='{' && c=='}'))
					{
						opstack.pop();
					}else{
						return false;
					}
				}

			}
			return opstack.empty();
    }
};