Leetcode #682: Baseball Game
In this guide, we solve Leetcode #682 Baseball Game in Python and focus on the core idea that makes the solution efficient.
You will see the intuition, the step-by-step method, and a clean Python implementation you can use in interviews.
Problem Statement
You are keeping the scores for a baseball game with strange rules. At the beginning of the game, you start with an empty record.
Quick Facts
- Difficulty: Easy
- Premium: No
- Tags: Stack, Array, Simulation
Intuition
The problem has a natural nested or last-in-first-out structure.
A stack lets us resolve matches in the correct order as we scan.
Approach
Push items as they appear and pop when you can finalize a decision.
The stack captures the unresolved part of the input.
Steps:
- Push elements as you scan.
- Pop when a rule or match is satisfied.
- Use the stack to compute results.
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.
Python Solution
class Solution:
def calPoints(self, operations: List[str]) -> int:
stk = []
for op in operations:
if op == "+":
stk.append(stk[-1] + stk[-2])
elif op == "D":
stk.append(stk[-1] << 1)
elif op == "C":
stk.pop()
else:
stk.append(int(op))
return sum(stk)
Complexity
The time complexity is , and the space complexity is . The space complexity is .
Edge Cases and Pitfalls
Watch for boundary values, empty inputs, and duplicate values where applicable. If the problem involves ordering or constraints, confirm the invariant is preserved at every step.
Summary
This Python solution focuses on the essential structure of the problem and keeps the implementation interview-friendly while meeting the constraints.