RPNAddSubHotFix.java

import java.util.LinkedList;

public class RPNAddSubHotFix {
  // @include
  public static int eval(String RPNExpression) {
    LinkedList<Integer> intermediateResults = new LinkedList<>();
    String delimiter = ",";
    String[] symbols = RPNExpression.split(delimiter);
    for (String token : symbols) {
      if (token.length() == 1 && "+-".contains(token)) {
        int y = intermediateResults.pop();
        int x = intermediateResults.pop();
        switch (token.charAt(0)) {
          case '+':
            intermediateResults.push(x + y);
            break;
          case '-':
            intermediateResults.push(x - y);
            break;
          default:
            throw new IllegalArgumentException("Malformed RPN at :" + token);
        }
      } else { // token is a number.
        intermediateResults.push(Integer.parseInt(token));
      }
    }
    return intermediateResults.pop();
  }
  // @exclude

  public static void main(String[] args) {
    assert (-5 == eval("5,10,-"));
    assert (6 == eval("-10,-16,-"));
    assert (12 == eval("10,2,+"));
    assert (15 == eval("1,2,+,3,4,*,+"));
    assert (42 == eval("1,2,3,4,5,+,*,+,+,3,4,*,+"));
    try {
        eval("-10,-2,/");
        assert(false);
    } catch (IllegalArgumentException e) {
        assert(true);
    }
  }
}