Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

ValidParentheses.cs

public class Solution {
    public bool IsValid(string s) {
     
        int len = s.Length;
        
        if(len == 0){
            return true;
        }
        
        var stack = new Stack<char>();
        for(int i=0;i<len;i++){
            
            if(s[i]=='(' || s[i] == '{' || s[i] == '['){
                stack.Push(s[i]);
            }
            else{
                
                if(stack.Count==0){
                    return false;
                }
                
                var c = stack.Pop();
                
                if(s[i] == ')' && c!='('){
                    return false;
                }
                if(s[i] == '}' && c!='{'){
                    return false;
                }
                if(s[i] == ']' && c!='['){
                    return false;
                }
            }
        }
        
        if(stack.Count!=0){
            return false;
        }
        
        return true;
        
    }
}