CODE

public class Solution {
  public bool IsValid(string s) {
    List<char> stack = new List<char>();
    for (int i = 0; i < s.Length; i++)
    {
      if (s[i] == '(' || s[i] == '[' || s[i] == '{')
        stack.Insert(0, s[i]);
      else if (s[i] == ')' && (stack.Count < 1 || stack[0] != '('))
        return false;
      else if (s[i] == ']' && (stack.Count < 1 || stack[0] != '['))
        return false;
      else if (s[i] == '}' && (stack.Count < 1 || stack[0] != '{'))
        return false;                
      else if (s[i] == ')' && stack[0] == '(')
        stack.RemoveAt(0);
      else if (s[i] == ']' && stack[0] == '[')
        stack.RemoveAt(0);
      else if (s[i] == '}' && stack[0] == '{')
        stack.RemoveAt(0);
    }
    if (stack.Count > 0)
      return false;
    return true;        
  }
}