circular left shift of an array by n positions in java

Question

I am trying to do the circular left shift of an array by n positions using only a single 1D array. I can do it in two arrays, but I haven\'t figured out how to do it using o

Answer 1

Here is the very easy algorithm, with O(1) Space in O(n)
Algorithm

• Reverse the array from 0 to n (numberOfPositions) positions
• Reverse the array from n+1 to array length - 1 positions
• Reverse the whole array from 0 to length - 1 positions

 public class ArrayRotator {

 private final int[] target;
 private final int length;

 public ArrayRotator(int[] seed) {
    this.target = seed;
    this.length = seed.length;
 }

 public void rotateInline(int numberOfPositions) {
    reverse(0, numberOfPositions);
    reverse(numberOfPositions + 1, length-1);       
    reverse(0, length-1);
 }

 private void reverse(int start, int end) {
    for (int i = start; i <= (start + end)/2; i++) {
        swap(i, start + end - i);
    }
 }

 private void swap(int first, int second) {
    int temp = this.target[second];
    this.target[second] = this.target[first];
    this.target[first] = temp;
 }
}

For example, lets say the array is [1,2,3,4] and n is 2
After step one, you would end up [2,1,3,4]
After Step two, you would end up [2,1,4,3]
After Step three, you would end up [3,4,1,2]