Algorithm to rotate an array in linear time

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You can do this in linear time by using a reverse() helper.

// rotate array of size=size, by n positions
void rotate(int array[], int size, int n)
{
  // reverse array[0...size-1]
  reverse(array, 0, size-1);

  // reverse A[0...n-1]
  reverse(array, 0, n-1);

  // reverse A[n...size-1]
  reverse(array, n, size-1);
}

// reverse elements in the array[pos_from ... pos_to]
void reverse(int array[], int pos_from, int pos_to)
{
   ...
}

Implementing reverse(int array[], int pos_from, int pos_to) using swaps is left as an exercise for the reader. Hint: This can be done in linear time.

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