2582. Pass the Pillow

Time: O(1)

Space: O(1)

Approach

Compute position via modular arithmetic on zigzag period of 2*(n-1).

Key Techniques

Array problems involve manipulating elements stored in a contiguous block of memory. Key techniques include two-pointer traversal, prefix sums, sliding windows, and in-place partitioning. In C#, arrays are zero-indexed and fixed in size — use List<T> when you need dynamic resizing.

Simulation

Simulation problems require implementing the described process step by step. Focus on correctly handling edge cases and state transitions. Common in geometry, game problems, and string manipulation. Optimize only if the naive simulation exceeds the time limit.

2582.cs

// Approach: Compute position via modular arithmetic on zigzag period of 2*(n-1).
// Time: O(1) Space: O(1)

public class Solution
{
    public int PassThePillow(int n, int time)
    {
        time %= (n - 1) * 2;

        if (time < n)
            return time + 1;

        return n - (time - (n - 1));
    }
}

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