Problem Overview & Intuition

Rotating an array of size N by K places can be solved in O(N) time and O(1) space using the reversal algorithm. By reversing sub-segments [0, k-1] and [k, n-1], and then the whole array, elements cycle into their target positions.

Step-by-Step Approach

1. Normalize k = k % n.
2. Reverse the first k elements: indices 0 to k - 1.
3. Reverse the remaining n - k elements: indices k to n - 1.
4. Reverse the entire array: indices 0 to n - 1.
5. Return arr.

Optimal Implementation (JavaScript)

function leftRotateByK(arr, k) {
  const n = arr.length;
  if (n <= 1) return arr;
  k = k % n;
  if (k === 0) return arr;

  function reverse(start, end) {
    while (start < end) {
      [arr[start], arr[end]] = [arr[end], arr[start]];
      start++;
      end--;
    }
  }

  reverse(0, k - 1);
  reverse(k, n - 1);
  reverse(0, n - 1);
  return arr;
}

Complexity Analysis