ValidParentheses.cs

// Source : https://leetcode.com/problems/valid-parentheses/ 
// Author : codeyu 
// Date : 2016年10月9日 14:37:53 

/***************************************************************************************
*
* 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.
* 
*
**********************************************************************************/

using System;
using System.Collections.Generic;
namespace Algorithms
{
    public class Solution020 
    {
        public static bool IsValid(string s) 
        {
            if(s.Length < 2 || s.Length % 2 != 0)
            {
                return false;
            }
            var left = "([{";
            var right = ")]}";
            var  st= new Stack<char>();
            foreach(var c in s)
            {
                if(left.IndexOf(c) != -1)
                {
                    st.Push(c);
                }
                else
                {
                    if(st.Count == 0 || st.Pop() != left[right.IndexOf(c)])
                    {
                        return false;
                    }
                }
            }
            return st.Count == 0;
        }
    }
}