Rotate an Array by K Positions

📌 Definition:

📖 Detailed Explanation:

The elegant O(1)-space trick is the reversal algorithm: reverse the whole array, then reverse the first k elements, then reverse the remaining n-k. Take k modulo n first so large k values wrap. O(n) time.

💻 Solutions:

• Java
• JavaScript
• Python

public static void rotate(int[] a, int k) {
    int n = a.length; k %= n;
    reverse(a, 0, n - 1);
    reverse(a, 0, k - 1);
    reverse(a, k, n - 1);
}
private static void reverse(int[] a, int i, int j) {
    while (i < j) { int t = a[i]; a[i++] = a[j]; a[j--] = t; }
}

function rotate(a, k) {
  const n = a.length; k %= n;
  const reverse = (i, j) => { while (i < j) { [a[i], a[j]] = [a[j], a[i]]; i++; j--; } };
  reverse(0, n - 1); reverse(0, k - 1); reverse(k, n - 1);
  return a;
}

def rotate(a, k):
    n = len(a)
    k %= n
    a[:] = a[-k:] + a[:-k] if k else a
    return a

🔑 Key Points:

• k %= n to handle k > n
• Reverse whole, then first k, then rest
• O(n) time, O(1) space
• Extra-array copy is the simpler O(n)-space variant

🌍 Real-World Example: