I would like to know how could I take in a negative value for d in the following code. This means, how could I traverse the array backwards and rotate its elements.
catchArray(int [] arr, int d)
{
int [] bArr = new int[arr.length];
for(int i = 0; i < bArr.length; i++)
{
bArr[(i + d) % bArr.length] = arr[i];
}
return bArr;
}
This is my answer for LeetCode Rotate Array assignment. Thank you in advance.
Just normalize "d" at the start of the program. If it's negative, then correct it.
Let's say the array length is 10 and d is -1. You'd get the same rotation if length was 10 and d was 9. That's all the adjustment at the start of the function is doing.
catchArray(int [] arr, int d)
{
d = d % arr.length;
if (d < 0)
{
d += arr.length;
}
int [] bArr = new int[arr.length];
for(int i = 0; i < bArr.length; i++)
{
bArr[(i + d) % bArr.length] = arr[i];
}
return bArr;
}
If the array is e.g. size 10, then a -1 rotation is the same as a +9 rotation.
In Java, the % remainder operator will return a negative value, if the quotient is negative, e.g. -12 % 10 and -2 % 10 will both return -2.
So, to get a normalized rotation value, we do this:
MIN_VALUE <= d <= MAX_VALUE
d % size -> -size < d < size
+ size -> 0 < d < size * 2
% size -> 0 <= d < size (normalized range)
Combined:
d = (d % arr.length + arr.length) % arr.length
That normalizes d to rotate less than one full round to the right.
static int[] catchArray(int[] arr, int d) {
d = (d % arr.length + arr.length) % arr.length;
int[] bArr = new int[arr.length];
for (int i = 0; i < arr.length; i++) {
bArr[(i + d) % arr.length] = arr[i];
}
return bArr;
}
Tests
System.out.println(Arrays.toString(catchArray(new int[] {1,2,3,4,5}, -8)));
System.out.println(Arrays.toString(catchArray(new int[] {1,2,3,4,5}, -2)));
System.out.println(Arrays.toString(catchArray(new int[] {1,2,3,4,5}, -1)));
System.out.println(Arrays.toString(catchArray(new int[] {1,2,3,4,5}, 0)));
System.out.println(Arrays.toString(catchArray(new int[] {1,2,3,4,5}, 1)));
System.out.println(Arrays.toString(catchArray(new int[] {1,2,3,4,5}, 2)));
System.out.println(Arrays.toString(catchArray(new int[] {1,2,3,4,5}, 8)));
Output
[4, 5, 1, 2, 3]
[3, 4, 5, 1, 2]
[2, 3, 4, 5, 1]
[1, 2, 3, 4, 5]
[5, 1, 2, 3, 4]
[4, 5, 1, 2, 3]
[3, 4, 5, 1, 2]
d?