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Java-based LeetCode algorithm problem solutions, regularly updated
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package g0601_0700.s0682_baseball_game;

// #Easy #Array #Stack #Simulation #2022_03_22_Time_4_ms_(57.60%)_Space_42.7_MB_(24.43%)

import java.util.ArrayList;
import java.util.List;

/**
 * 682 - Baseball Game\.
 *
 * Easy
 *
 * 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 i^th operation you must apply to the record and is one of the following:
 *
 * 1.  An integer `x` - Record a new score of `x`.
 * 2.  `"+"` - Record a new score that is the sum of the previous two scores. It is guaranteed there will always be two previous scores.
 * 3.  `"D"` - Record a new score that is double the previous score. It is guaranteed there will always be a previous score.
 * 4.  `"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_.
 *
 * **Example 1:**
 *
 * **Input:** ops = ["5","2","C","D","+"]
 *
 * **Output:** 30
 *
 * **Explanation:** 
 *
 *     "5" - Add 5 to the record, record is now [5]. 
 *     "2" - Add 2 to the record, record is now [5, 2]. 
 *     "C" - Invalidate and remove the previous score, record is now [5]. 
 *     "D" - Add 2 \* 5 = 10 to the record, record is now [5, 10]. 
 *     "+" - Add 5 + 10 = 15 to the record, record is now [5, 10, 15]. 
 *     The total sum is 5 + 10 + 15 = 30.
 *
 * **Example 2:**
 *
 * **Input:** ops = ["5","-2","4","C","D","9","+","+"]
 *
 * **Output:** 27
 *
 * **Explanation:** 
 *
 *     "5" - Add 5 to the record, record is now [5]. 
 *     "-2" - Add -2 to the record, record is now [5, -2]. 
 *     "4" - Add 4 to the record, record is now [5, -2, 4]. 
 *     "C" - Invalidate and remove the previous score, record is now [5, -2]. 
 *     "D" - Add 2 \* -2 = -4 to the record, record is now [5, -2, -4]. 
 *     "9" - Add 9 to the record, record is now [5, -2, -4, 9]. 
 *     "+" - Add -4 + 9 = 5 to the record, record is now [5, -2, -4, 9, 5]. 
 *     "+" - Add 9 + 5 = 14 to the record, record is now [5, -2, -4, 9, 5, 14]. 
 *     The total sum is 5 + -2 + -4 + 9 + 5 + 14 = 27.
 *
 * **Example 3:**
 *
 * **Input:** ops = ["1"]
 *
 * **Output:** 1
 *
 * **Constraints:**
 *
 * *   `1 <= ops.length <= 1000`
 * *   `ops[i]` is `"C"`, `"D"`, `"+"`, or a string representing an integer in the range [-3 * 10⁴, 3 * 10⁴].
 * *   For operation `"+"`, there will always be at least two previous scores on the record.
 * *   For operations `"C"` and `"D"`, there will always be at least one previous score on the record.
**/
public class Solution {
    public int calPoints(String[] ops) {
        List resultList = new ArrayList<>(ops.length);
        for (String op : ops) {
            int size = resultList.size();
            if ("C".equals(op)) {
                resultList.remove(size - 1);
            } else if ("D".equals(op)) {
                resultList.add(resultList.get(size - 1) * 2);
            } else if ("+".equals(op)) {
                resultList.add(resultList.get(size - 1) + resultList.get(size - 2));
            } else {
                resultList.add(Integer.parseInt(op));
            }
        }
        return resultList.stream().reduce(0, Integer::sum);
    }
}