Baseball Game

Problem Description

You are keeping the scores for a baseball game with strange rules. You are given a list of strings operations, where operations[i] is the i-th operation you must apply to the record and is one of the following: an integer x (record a new score of x), '+' (record a new score that is the sum of the previous two scores), 'D' (record a new score that is the double of the previous score), or 'C' (invalidate the previous score, removing it from the record). Return the sum of all the scores on the record after applying all the operations.

Key Insights

• The operations can involve recording a score, summing two previous scores, doubling the last score, or canceling the last score.
• A stack can be effectively used to keep track of the scores and apply the operations in order.
• The constraints guarantee valid operations, meaning we won't face out-of-bounds issues with our stack.

Space and Time Complexity

Time Complexity: O(n), where n is the number of operations, since we process each operation exactly once. Space Complexity: O(n), in the worst case where all operations are valid scores, we store all scores in the stack.

Solution

To solve the problem, we can use a stack data structure to keep track of the scores. We will iterate through the list of operations and perform the following actions based on the type of operation:

1. If the operation is an integer, we will convert it to an integer and push it onto the stack.
2. If the operation is '+', we will sum the last two scores from the stack and push the result onto the stack.
3. If the operation is 'D', we will double the last score from the stack and push the result onto the stack.
4. If the operation is 'C', we will pop the last score from the stack, effectively invalidating it. Finally, we will sum all the scores in the stack and return the total.

Code Solutions