Problem Overview & Intuition

In left rotation by one place, the first element cycles to the end, while every other element moves one index to the left (i -> i - 1). This is done in-place with a temporary variable storing the first element.

Step-by-Step Approach

1. If arr.length <= 1, return arr immediately.
2. Store the first element: const first = arr[0];.
3. Iterate from i = 0 to arr.length - 2, setting arr[i] = arr[i + 1].
4. Set arr[arr.length - 1] = first.
5. Return arr.

Optimal Implementation (JavaScript)

function leftRotateByOne(arr) {
  if (arr.length <= 1) return arr;
  const first = arr[0];
  for (let i = 0; i < arr.length - 1; i++) {
    arr[i] = arr[i + 1];
  }
  arr[arr.length - 1] = first;
  return arr;
}

Complexity Analysis