682. Baseball Game

Problem Link

Description

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You are keeping the scores for a baseball game with strange rules. At the beginning of the game, you start with an empty record.

You are given a list of strings operations, where operations[i] is the ith operation you must apply to the record and is one of the following:

• An integer x.

  <ul>
  	<li>Record a new score of <code>x</code>.</li>
  </ul>
  </li>
  <li><code>&#39;+&#39;</code>.
  <ul>
  	<li>Record a new score that is the sum of the previous two scores.</li>
  </ul>
  </li>
  <li><code>&#39;D&#39;</code>.
  <ul>
  	<li>Record a new score that is the double of the previous score.</li>
  </ul>
  </li>
  <li><code>&#39;C&#39;</code>.
  <ul>
  	<li>Invalidate the previous score, removing it from the record.</li>
  </ul>
  </li>
  

Return the sum of all the scores on the record after applying all the operations.

The test cases are generated such that the answer and all intermediate calculations fit in a 32-bit integer and that all operations are valid.

 

Example 1:

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 2:

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 3:

Input: ops = ["1","C"]
Output: 0
Explanation:
"1" - Add 1 to the record, record is now [1].
"C" - Invalidate and remove the previous score, record is now [].
Since the record is empty, the total sum is 0.

 

Constraints:

• 1 <= operations.length <= 1000
• operations[i] is "C", "D", "+", or a string representing an integer in the range [-3 * 104, 3 * 104].
• 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.

Solution

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Python3

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