Rotate Array

Problem

Given an integer array nums, rotate it to the right by k steps. Do it in place with O(1) extra memory.

Constraints

• 1 ≤ length ≤ 10⁵
• 0 ≤ k ≤ 10⁵

Approach — Two Pointers

This is a Two Pointers problem. The idea: walk two indices through the data together (or toward each other), turning an O(n²) pair search into one linear pass. Work through the reference code below line by line, then re-derive it yourself in the editor — that's how the pattern sticks.

Complexity: O(n) time, O(1) extra space.

Solution code

Python

class Solution:
    def rotate(self, nums, k):
        n = len(nums)
        k %= n
        nums[:] = nums[-k:] + nums[:-k] if k else nums
        return nums

Java

class Solution {
    public void rotate(int[] nums, int k) {
        int n = nums.length;
        k %= n;
        reverse(nums, 0, n - 1);
        reverse(nums, 0, k - 1);
        reverse(nums, k, n - 1);
    }
    private void reverse(int[] a, int l, int r) {
        while (l < r) { int t = a[l]; a[l++] = a[r]; a[r--] = t; }
    }
}

Practice it

Reading a solution isn't the same as being able to write it under pressure. Open this problem in the in-browser editor, hide the solution, and solve it from scratch — your code runs against real test cases instantly.