/**
 * 682. Baseball Game
 * 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.
 *
 * Refer to: 2203/220326-CN.cpp
 */