C/C++ - efficient method of rotating an array without using build-in functions (homework)

Question

The task is to rotate left or rotate right a subarray of an array given number of times.

Let me explain this on an example:

• lets data be an array.

Answer 1

There's a trick to this. It's pretty weird that you'd get this for homework if the trick wasn't mentioned in class. Anyway...

To rotate a sequence of N elements left by M:

• reverse the whole sequence
• reverse the last M elements
• reverse the first N-M elements

done

e.g. left by 2: 1234567 -> 7654321 -> 7654312 -> 3456712