Leetcode #2582: Pass the Pillow
In this guide, we solve Leetcode #2582 Pass the Pillow 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
There are n people standing in a line labeled from 1 to n. The first person in the line is holding a pillow initially.
Quick Facts
- Difficulty: Easy
- Premium: No
- Tags: Math, Simulation
Intuition
There is a mathematical invariant or formula that directly leads to the result.
Using math avoids unnecessary loops and reduces complexity.
Approach
Derive the formula or update rule, then compute the answer directly.
Handle edge cases like overflow or zero carefully.
Steps:
- Identify the math relationship.
- Compute the result with a loop or formula.
- Handle edge cases.
Example
Input: n = 4, time = 5
Output: 2
Explanation: People pass the pillow in the following way: 1 -> 2 -> 3 -> 4 -> 3 -> 2.
After five seconds, the 2nd person is holding the pillow.
Python Solution
class Solution:
def passThePillow(self, n: int, time: int) -> int:
ans = k = 1
for _ in range(time):
ans += k
if ans == 1 or ans == n:
k *= -1
return ans
Complexity
The time complexity is and the space complexity is , where is the given time. The space complexity is , where is the given time.
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.