https://leetcode.com/problems/valid-parentheses/

ValidParentheses.cs

public class Solution 
{
  public bool IsValid(string s) 
    {
        if (s == null || s.Length % 2 != 0) { return false; }
        if (s == string.Empty) { return true; }
        var isOpenDict = new Dictionary<string, bool> { { "(", true }, { "{", true }, { "[", true }, { ")", false }, { "}", false }, { "]", false } };
        var matches = new Dictionary<string, string> { { "(", ")" }, { "{", "}" }, { "[", "]" } };
        var nested = new List<string>();
        for (var i = 0; i < s.Length; i++)
        {
            if (isOpenDict[s[i].ToString()])
            {
                nested.Add(s[i].ToString());
            }
            else
            {
                if (nested.Count == 0) { return false; }
                if (matches[nested[nested.Count - 1]] == s[i].ToString())
                {
                    nested.RemoveAt(nested.Count - 1);
                    continue;
                }
                return false;
            }
        }
        if (nested.Count > 0) { return false; }
        return true;
    }
}