text: # You are keeping score for a baseball game with strange rules. The game consists of several rounds, where the scores of past rounds may affect future rounds' scores.
  
  # At the beginning of the game, you start with an empty record. You are given a list of strings ops, where ops[i] is the ith operation you must apply to the record and is one of the following:
  
  # An integer x - Record a new score of x.
  # "+" - Record a new score that is the sum of the previous two scores. It is guaranteed there will always be two previous scores.
  # "D" - Record a new score that is double the previous score. It is guaranteed there will always be a previous score.
  # "C" - Invalidate the previous score, removing it from the record. It is guaranteed there will always be a previous score.
  # Return the sum of all the scores on the record.
  class Solution {
      public int calPoints(String[] ops) {
          Stack<Integer> stack = new Stack();
  
          for(String op : ops) {
              if (op.equals("+")) {
                  int top = stack.pop();
                  int newtop = top + stack.peek();
                  stack.push(top);
                  stack.push(newtop);
              } else if (op.equals("C")) {
                  stack.pop();
              } else if (op.equals("D")) {
                  stack.push(2 * stack.peek());
              } else {
                  stack.push(Integer.valueOf(op));
              }
          }
  
          int ans = 0;
          for(int score : stack) ans += score;
          return ans;
      }
  }
  