BaseballGame.js

// Source : https://leetcode.com/problems/baseball-game
// Author : Dean Shi
// Date   : 2017-09-24

/***************************************************************************************
 * 
 * You're now a baseball game point recorder
 * 
 * Given a list of strings, each string can be one of the 4 following types
 * 
 * Integer (one round's score): Directly represents the number of points you get in
 * this round
 * "+" (one round's score): Represents that the points you get in this round are the
 * sum of the last two valid round's points
 * "D" (one round's score): Represents that the points you get in this round are the
 * doubled data of the last valid round's points
 * "C" (an operation, which isn't a round's score): Represents the last valid round's
 * points you get were invalid and should be removed
 * 
 * Each round's operation is permanent and could have an impact on the round before and
 * the round after
 * 
 * You need to return the sum of the points you could get in all the rounds
 * 
 * Example 1
 * Input: ["5","2","C","D
 * Output: 15
 * Explanation
 * Round 1: You could get 5 points. The sum is: 5
 * Round 2: You could get 2 points. The sum is: 7
 * Operation 1: The round 2's data was invalid. The sum is: 5
 * Round 3: You could get 10 points (the round 2's data has been removed). The sum is:
 * 15
 * Round 4: You could get 5 + 10 = 15 points. The sum is: 30
 * 
 * Example 2
 * Input: ["5","-2","4","C","D","9
 * Output: 27
 * Explanation
 * Round 1: You could get 5 points. The sum is: 5
 * Round 2: You could get -2 points. The sum is: 3
 * Round 3: You could get 4 points. The sum is: 7
 * Operation 1: The round 3's data is invalid. The sum is: 3
 * Round 4: You could get -4 points (the round 3's data has been removed). The sum is
 * : -1
 * Round 5: You could get 9 points. The sum is: 8
 * Round 6: You could get -4 + 9 = 5 points. The sum is 13
 * Round 7: You could get 9 + 5 = 14 points. The sum is 27
 * 
 * Note
 * The size of the input list will be between 1 and 1000
 * Every integer represented in the list will be between -30000 and 30000
 * 
 ***************************************************************************************/

/**
 * @param {string[]} ops
 * @return {number}
 */
var calPoints = function(ops) {
    const arr = []
    const actions = {
        C: () => arr.pop(),
        D: () => arr.push(arr[arr.length - 1] * 2),
        '+': () => arr.push(arr[arr.length - 1] + arr[arr.length - 2])
    }
    for (let a of ops) {
        a in actions ? actions[a](): arr.push(+a)
    }
    return arr.reduce((sum, num) => sum + num)
};