Working solution in C++: /* Rotate vector x [n] left by d positions. For n=8 and d=3, change abcdefgh to defghabc (123456789 to 456789123) Constraints: O(n) time, O( 1 ) extra space. */ #include using namespace std; void reverse(int arr[], int start, int end) { const int mid = (start + end)/2; for (int i = start, offset = 0; i <= mid; ++i, ++offset) { const int temp = arr[i]; arr[i] = arr[end-offset]; arr[end-offset] = temp; } } void rotateArr(int arr[], int n, int d) { // 1. Rotate the entire array reverse(arr, 0, n-1); // 2. Rotate 0 to k-1 const int k = (n-d); reverse(arr, 0, k-1); // 3. Rotate k to n-1 reverse(arr, k, n-1); } int main() { int arr[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9 }; const int size = sizeof(arr)/sizeof(int); cout << "before:\n"; for (int i = 0; i < size; ++i) cout << arr[i] << " "; cout << endl << endl; // rotate int d = 3; rotateArr(arr, size, d); cout << "after:\n"; for (int i = 0; i < size; ++i) cout << arr[i] << " "; cout << endl << endl; }