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24. Rotate Array

mediumAsked at Workday

Rotate an array to the right by k steps. Workday uses this to test in-place transformation discipline — same shape as shifting a payroll cycle's days when a holiday lands mid-period.

By Alex Chen, Founder, InterviewChamp.AI · Last verified

Source citations

Public interview reports confirming this problem appears in Workday loops.

  • Glassdoor (2025)— Workday SDE2 phone screen.

Problem

Given an integer array nums, rotate the array to the right by k steps, where k is non-negative.

Constraints

  • 1 <= nums.length <= 10^5
  • -2^31 <= nums[i] <= 2^31 - 1
  • 0 <= k <= 10^5
  • Follow-up: Could you do it in-place with O(1) extra space?

Examples

Example 1

Input
nums = [1,2,3,4,5,6,7], k = 3
Output
[5,6,7,1,2,3,4]

Example 2

Input
nums = [-1,-100,3,99], k = 2
Output
[3,99,-1,-100]

Approaches

1. Extra array

Copy nums[i] -> result[(i + k) % n]. Copy result back.

Time
O(n)
Space
O(n)
const n = nums.length;
const r = new Array(n);
for (let i=0;i<n;i++) r[(i+k)%n] = nums[i];
for (let i=0;i<n;i++) nums[i] = r[i];

Tradeoff: Easy but O(n) extra space — fails the follow-up.

2. Three reverses

Reverse the whole array, reverse the first k, reverse the rest. (k mod n first.)

Time
O(n)
Space
O(1)
function rotate(nums, k) {
  const n = nums.length;
  k = k % n;
  function reverse(i, j) {
    while (i < j) { [nums[i], nums[j]] = [nums[j], nums[i]]; i++; j--; }
  }
  reverse(0, n - 1);
  reverse(0, k - 1);
  reverse(k, n - 1);
}

Tradeoff: O(1) space. The trick: reversing the whole array puts the would-be tail at the head; then reversing each half restores intra-segment order.

Workday-specific tips

Workday wants the in-place version. State 'k mod n first' explicitly — otherwise you'd do extra work for k > n. The three-reverse trick is what they're testing.

Common mistakes

  • Forgetting k = k % n — k can exceed n.
  • Reversing in the wrong order — must be whole, then [0, k-1], then [k, n-1].
  • Off-by-one on reverse bounds (using k instead of k-1).

Follow-up questions

An interviewer at Workday may pivot to one of these next:

  • Rotate by k to the LEFT — same idea, reversed.
  • Rotate a string (LC 796 — substring of doubled string).
  • Rotate a 2D matrix (LC 48).

Solve it now

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Output

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FAQ

Why three reverses?

Reversing the whole array swaps suffix with prefix relative to position k. Each half is now in reverse order, so reversing each restores original ordering.

Cyclic-replace alternative?

Yes — start at index 0, place its value at (0+k)%n, place THAT value at (k+k)%n, until you cycle back. Use gcd(n,k) loops. Works but trickier to write correctly.

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