LeetCode -- Valid Parentheses

题目描述：
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.




在一个只包含"()[]{}"的输入中，判断括号的合法性。


思路：
栈的基本使用。


实现代码：

public class Solution {
    public bool IsValid(string s) 
    {
        var stack = new Stack<char>();
	
    	for(var i = 0;i < s.Length; i++){
    		switch(s[i]){
    			case '{':
    			case '[':
    			case '(':
    				stack.Push(s[i]);
    				break;
    			case '}':
    				if(stack.Count > 0 && stack.Peek() == '{'){
    					stack.Pop();
    				}
    				else{
    					return false;
    				}
    				break;
    			case ']':
    				if(stack.Count > 0 && stack.Peek() == '['){
    					stack.Pop();
    				}
    				else{
    					return false;
    				}
    				break;
    			case ')':
    				if(stack.Count > 0 && stack.Peek() == '('){
    					stack.Pop();
    				}
    				else{
    					return false;
    				}
    				break;
    			default :
    				throw new ArgumentException(s);
    		}
    	}
    	
    	return stack.Count == 0;
    }
}