src/main/java/com/fishercoder/solutions/_682.java

package com.fishercoder.solutions;

import java.util.Stack;

public class _682 {

    public static class Solution1 {
        public int calPoints(String[] ops) {
            Stack<Integer> stack = new Stack<>();
            int sum = 0;
            int firstLast = Integer.MIN_VALUE;
            int secondLast = Integer.MIN_VALUE;
            for (String op : ops) {
                if (op.equals("+")) {
                    if (!stack.isEmpty()) {
                        firstLast = stack.pop();
                    }
                    if (!stack.isEmpty()) {
                        secondLast = stack.pop();
                    }
                    int thisRoundPoints = firstLast + secondLast;

                    if (secondLast != Integer.MIN_VALUE) {
                        stack.push(secondLast);
                    }
                    if (firstLast != Integer.MIN_VALUE) {
                        stack.push(firstLast);
                    }
                    stack.push(thisRoundPoints);
                    sum += thisRoundPoints;

                    firstLast = Integer.MIN_VALUE;
                    secondLast = Integer.MIN_VALUE;
                } else if (op.equals("D")) {
                    if (!stack.isEmpty()) {
                        int thisRoundPoints = stack.peek() * 2;
                        stack.push(thisRoundPoints);
                        sum += thisRoundPoints;
                    }
                } else if (op.equals("C")) {
                    if (!stack.isEmpty()) {
                        int removedData = stack.pop();
                        sum -= removedData;
                    }
                } else {
                    Integer val = Integer.parseInt(op);
                    sum += val;
                    stack.push(val);
                }
            }
            return sum;
        }
    }
}