将数组的所有元素向左旋转“ k”位置，但我的代码将其向右移动

Question

Can someone tell how to fix this code so instead of moving the arrays to the right how do i make it move to the left? Can someone please explain it to me too

public class Test {
  public static void main(String[] args) {
    int[] b = {10, 20, 30, 40, 50, 60};
    System.out.println("\n///// Rotate Left k cell example \n////");
    b = copyArray(a, a.length); 
    b = rotateLeft(b,4); //assuming k = 4
    printArray(b); // This Should Print: { 50, 60, 10, 20, 30, 40 };
  }

  // Rotates all the elements of the source array to the right by 'k' positions
  // Returns the updated array
  public static int[] rotateLeft(int[] source, int k) {
    int[] arr = copyArray(source,source.length); //copies all source to a new array
    int[] temp = new int[arr.length];

    for (int i = 0; i < arr.length; i++){
      temp[(i + k) % arr.length] = arr[i];
    }

    for (int i = 0; i < arr.length; i++){
      arr[i] = temp[i];
    }

    return arr; 
  }
}

So this code rotates the elements to the right side. How should i modify it so that it rotates it to the left side?
Output i am getting:

{ 30, 40, 50, 60, 10, 20 }

but my desired output is:

{ 50, 60, 10, 20, 30, 40 }

Answer 1

I think you can just change your assignment logic for populating the temp array. Change this line:

temp[(i + k) % arr.length] = arr[i];

to this:

temp[i] = arr[(i + k) % arr.length];

The logic here is that the ith entry in temp[] will equal the entry k steps ahead of it in arr[] . In other words, temp[] will contain the original elements shifted to the left by k . Note that you still need the mod operation to make sure that indexing wraps around the size of the array.

Full code:

public static int [] rotateLeft(int [] source, int k){
    int arr[] = copyArray(source, source.length);
    int[] temp = new int[arr.length];
    for (int i=0; i<arr.length; i++) {
        temp[i] = arr[(i + k) % arr.length];
    }
    for (int i=0; i<arr.length; i++) {
        arr[i] = temp[i];
    }

    return arr; 
}

Answer 2

Basically do (i - k) instead of (i + k) . On top of that, remove the copyArray call and the second loop. And because the % operator in java behaves the it does, you have to add source.length to (i - k) before actually % ing it:

public static int [] rotateLeft(int [] source, int k) {
    int arr[] = new int[source.length];

    for (int i = 0; i < arr.length; i++){
        arr[(i - k + source.length) % source.length] = source[i];
    }

    return arr; 
}

Outputting

50
60
10
20
30
40