682. Baseball Game 棒球比赛计分

You're now a baseball game point recorder.

Given a list of strings, each string can be one of the 4 following types:

1. Integer (one round's score): Directly represents the number of points you get in this round.
2. "+" (one round's score): Represents that the points you get in this round are the sum of the last two valid round's points.
3. "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.
4. "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

给定一个字符串列表，每个字符串可以是以下4种类型之一： 

整数（一轮的得分）：直接代表你在这一轮中获得的积分数。 

“+”（一轮的得分）：表示你在这一轮中获得的积分是最后两个有效回合点的总和。

“D”（一轮的得分）：表示您在本轮获得的积分是上次有效回合点数的双倍数据。

“C”（一个不是一轮的得分的操作）：表示最后一次有效回合的得分无效，应该被删除。 

每轮的运作是永久性的，可能会对前一轮和之后的一轮产生影响。 

您需要返回所有回合中可以得到的积分总和。

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

来自为知笔记(Wiz)