Practice eBay Coding Question | Real Coding Interviews

Quick Summary

Find the number of right cyclic shifts required to transform a given permutation into the strictly descending sequence [n, n-1, ..., 1].
Return -1 if no valid shift exists to achieve the target ordering.
The problem emphasizes validating index transformations rather than performing explicit array rotations.

What This Tests

Array simulation and traversal
Modular arithmetic for cyclic indexing
Early termination and constraint validation
Direct index-to-value mapping verification

Common Patterns

Simulation

Array Manipulation

For an array nums of length n and a non-negative integer t with 0 ≤ t < n, a cyclic t-shift of nums is the array obtained by taking the last t elements of nums and moving them, in order, to the front. Concretely:

t = 0 leaves the array unchanged: [nums[0], nums[1], ..., nums[n-1]].
t = 1 produces [nums[n-1], nums[0], nums[1], ..., nums[n-2]].
t = 2 produces [nums[n-2], nums[n-1], nums[0], nums[1], ..., nums[n-3]].
t = n-1 produces [nums[1], nums[2], ..., nums[n-1], nums[0]].

Test Cases

Input

Output

Expected