In Place rotation C++ Practice

Question

I have a working rotating function going for my "items" int array. The code below gets it done, except that im transferring values out unnecessarily. Im trying to acheive the "inplace" rotation. What I mean by that is where the ptrs would increment or decrement instead of grabbing values out of the array..By which I need to "up" the efficiency level in that way for this method..Any Suggestions?

void quack::rotate(int nRotations)
{
 if ( count <= 1 ) return;
 else  // make sure our ptrs are where we want them.
 {
  intFrontPtr = &items[0].myInt;
  intBackPtr  = &items[count-1].myInt;
 }
 for (int temp = 0; nRotations != 0;)
 {
  if ( nRotations > 0 )
  {
     temp = *intFrontPtr;
    *intFrontPtr = *intBackPtr;
    *intBackPtr  = temp; // Connect temps for the rotation
   --intBackPtr; // Move left [...<-] into the array
  }
  else if ( nRotations < 0 ) 
  {
   temp = *intBackPtr;
   *intBackPtr  = *intFrontPtr;
   *intFrontPtr = temp; // Connect temps for the rotation
   ++intFrontPtr; // Move right [->...] into the array
  }
  if ( intBackPtr  == &items[0].myInt  || 
    intFrontPtr == &items[count-1].myInt ) 
  {
   intFrontPtr = &items[0].myInt; 
   intBackPtr  = &items[count-1].myInt; // need to re-set
   if ( nRotations > 0 ) nRotations--;  // Which ways did we rotate?
   else nRotations++;
  }
 }
 }

Oh yes, Im trying to practice c++ and know their are many functions floating around that are programmed to do this already...Im trying to "build my own". I think i've got it down syntactically, but the efficiency is always where i struggle. As, a novice, I would greatly appreciate critisim towards this aspect..

Answer 1

https://stackoverflow.com/q/17119000/2383578 : This is somewhat similar to what is discussed here. Rotating the array by a particular amount.

Answer 2

There is an old trick for rotating elements in an array (I first saw it in Programming Pearls)

Say you want to rotate an array to the left by three elements.

First reverse the first three elements, next reverse the remaining elements, and then reverse the entire array.

Starting Array:
1 2 3 4 5 6 7

After reversing the first three elements
3 2 1 4 5 6 7

After reversing the remaining elements
3 2 1 7 6 5 4

Finally reverse the entire array to get the final rotated array
4 5 6 7 1 2 3

Reversing portions of the array can be done in place so you don't need any extra memory.

Answer 3

Here's one that I got by modifying the code here:

template<class It>
It rotate(It begin, It const middle, It end)
{
    typename std::iterator_traits<It>::difference_type i = 0, j;
    if (begin != middle && middle != end)
    {
        while ((i = std::distance(begin, middle)) !=
               (j = std::distance(middle,   end)))
        {
            It k = middle;
            std::advance(
                k,
                std::max(typename std::iterator_traits<It>::difference_type(),
                j - i));
            std::swap_ranges(k, end, begin);
            if (i > j) { std::advance(begin, j); }
            else { std::advance(end, -i); }
        }
    }
    return std::swap_ranges(middle - i, middle, middle);
}

Answer 4

Here is code for sdtom solution

void rotateArray(int arr[], int low, int high)
{
    while  (low<high) {
        int temp = arr[low];
        arr[low]=arr[high];
        arr[high]=temp;
        low++;
        high--;
    }
}
void rotate (int arr[], int k,int uperLimit)
{
    rotateArray(arr,0,k);
    rotateArray(arr,k+1,uperLimit-1);
    rotateArray(arr,0,uperLimit-1);

}