Problem description

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.

Solution

This problem can be solved by stack which keep track of points of all valid round and sum of total points. Below is python implementation

class Solution:
    def calPoints(self, ops: List[str]) -> int:
        sm = 0
        stack = []
        for op in ops:
            if op == "C":
                sm -= stack.pop()
            elif op == "D":
                current = 2 * stack[-1]
                sm += current
                stack.append(current)
            elif op == "+":
                current = stack[-1] + stack[-2]
                sm += current
                stack.append(current)
            else:
                current = int(op)
                sm += current
                stack.append(current)
        return sm