Description of reverse

[EvanGertis]

Thank you for publishing your work on this algorithm. It is very fascinating. I am reading Chapter 1. I would just like to get some clarification about the reverse method. I know that the method is simple, but does this really do what it says it does? I have written a small example to test it.

public class WikiSortTest{

    static class Range{
        public int start;
        public int end;

        public Range(int start1, int end1){
            start = start1;
            end = end1;
        }

        public Range(){
            start =0;
            end =0;
        }

        void set(int start1, int end1){
            start = start1;
            end = end1;
        }

        int length(){
            return end-start;
        }

    }

    static void swap(int[] A, int i, int j){
        int temp = A[i];
        A[i] = A[j];
        A[j] = temp;
    }

    static void reverse(int[] A, Range range){
        for(int index=range.length()/2 -1; index >=0; index--){
            swap(A,A[range.start+index],A[range.end-index-1]);
        }
    }

    static void printArray(int[] A){
        System.out.println();
        for(int i=0; i < A.length; i++){
            System.out.printf(A[i]+" | ");
        }
        System.out.println();
    }

    public static void main(String[] args){
        int[] A = new int[]{0,1,2,3,4};
        printArray(A);
        Range range = new Range(0,3);
        reverse(A,range);
        printArray(A);
    }
}

The output from this program is

PS D:\Algorithm Analysis> javac WikiSortTest.java
PS D:\Algorithm Analysis> java WikiSortTest      

0 | 1 | 2 | 3 | 4 | 

2 | 1 | 0 | 3 | 4 |

Is this to be expected?

[BonzaiThePenguin]

Hi there, so the reverse function takes a range within the array and reverses that range. The ranges are considered exclusive so Range(0, 3) means >= index 0 and < index 3. In the example you can see it reversed the first 3 items and left items outside that range untouched. Sorry if that wasn't clear in the docs.