20. Valid Parentheses

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本文介绍了一个使用栈数据结构实现的有效括号匹配验证算法。该算法能够判断字符串中的括号是否正确配对，包括圆括号'()'、方括号'[]'及花括号'{}

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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.

#include <iostream>
#include <stack>

using namespace std;

class Solution {
public:
	bool isValid(string s) {
		stack<char> stk; 
		char c;
		for (int i = 0; i < s.length(); ++i)
		{
			if (stk.empty() )
			{
				if (s[i] != '(' && s[i] != '{' && s[i] != '[') return false;
				else stk.push(s[i]); 
				continue; 
			}
			c = stk.top();
			switch(s[i])
			{
			case ')':
				if (c == '(') stk.pop();
				else stk.push(s[i]);
				break;
			case '}':
				if (c == '{') stk.pop();
				else stk.push(s[i]);
				break;
			case  ']' :
				if (c == '[') stk.pop();
				else  stk.push(s[i]);
				break;
			default:
				stk.push(s[i]);
				break;
			}

		}
		if (stk.empty())
			return true;
		else
			return false;
 
	}
};


int main()
{
	Solution a;
	cout << a.isValid("(])") << endl;
	system("pause");
	return 0;
}