How can we rotate an array to the left?

Question

EX: I have an array {1, 2, 3, 4, 5} and an integer number 7 It will rotate 7 spaces to the right like: {4, 5, 1, 2, 3}

I also have that array {1, 2, 3, 4, 5} and an integer number -7 It will rotate 7 spaces to the left like: {3, 4, 5, 1, 2}

I have rotated the array to the right by using:

for(int i = 0; i < data.length; i++){
              result[(i+n) % data.length ] = data[i];
            }

But how can we rotate an array to the left?

Answer 1

Rotating to the left by n is the same as rotating to the right by length-n.

Rotate right (for positive n):

for(int i = 0; i < data.length; i++){
    result[(i+n) % data.length ] = data[i];
}

Rotate left (for positive n):

for(int i = 0; i < data.length; i++){
    result[(i+(data.length-n)) % data.length ] = data[i];
}

This way you can avoid a modulo of a negative number.

If you want to input an integer n that rotates right if n is positive and left if n is negative, you can do it like this:

 int[] rotateArray(int n, int[] data)
 {
      if(n < 0) // rotating left?
      {
          n = -n % data.length; // convert to +ve number specifying how 
                                // many positions left to rotate & mod
          n = data.length - n;  // rotate left by n = rotate right by length - n
      }
      int[] result = new int[data.length];
      for(int i = 0; i < data.length; i++){
          result[(i+n) % data.length ] = data[i];
      }
      return result;
 }