CODE

public class Solution {
  public int EvalRPN(string[] tokens) {
    List<int> stack = new List<int>();

    int eval = 0;

    for (int i = 0; i < tokens.Length; i++)
    {
      if (tokens[i] != "+" && tokens[i] != "-" && tokens[i] != "*" && tokens[i] != "/")
        stack.Insert(0, Convert.ToInt32(tokens[i]));
      else if (tokens[i] == "+")
      {
        eval = stack[0] + stack[1];
        stack.RemoveAt(0);
        stack.RemoveAt(0);
        stack.Insert(0, eval);              
      }
      else if (tokens[i] == "-")
      {
        eval = stack[1] - stack[0];
        stack.RemoveAt(0);
        stack.RemoveAt(0);
        stack.Insert(0, eval);              
      }
      else if (tokens[i] == "*")
      {
        eval = stack[0] * stack[1];
        stack.RemoveAt(0);
        stack.RemoveAt(0);
        stack.Insert(0, eval);                                
      }
      else if (tokens[i] == "/")
      {
        eval = stack[1] / stack[0];
        stack.RemoveAt(0);
        stack.RemoveAt(0);
        stack.Insert(0, eval);                              
      }
    }
    return stack[0];
  }

}