682.BaseballGame.py

"""
    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:
        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:
    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:
    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:
    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 * 10**4, 3 * 10**4].
        - 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.
"""
#Difficulty: Easy
#39 / 39 test cases passed.
#Runtime: 36 ms
#Memory Usage: 14.1 MB

#Runtime: 36 ms, faster than 85.56% of Python3 online submissions for Baseball Game.
#Memory Usage: 14.1 MB, less than 100.00% of Python3 online submissions for Baseball Game.

class Solution:
    def calPoints(self, ops: List[str]) -> int:
        scores = []
        for n in ops:
            if n == "+":
                scores.append(scores[-1] + scores[-2])
            elif n == "D":
                scores.append(scores[-1] * 2)
            elif n == "C":
                scores.pop()
            else:
                scores.append(int(n))
        return sum(scores)