MergeSort.java

package sorts;

/**
 * MergeSort.java
 * Created by Stijn Strickx on May 21, 2008
 * Copyright 2008 Stijn Strickx, All rights reserved
 */

/**
 * Merge sort algorithm
 * Average Time Complexity: O(n log n)
 * Worst Time Complexity: O(n log n)
 * Memory Complexity: O(n)
 * Stable: yes
 */

public class MergeSort extends Sorter{

    @Override
    public <T extends Comparable<? super T>> void sort(T[] a) {
        // Generic array creation is not possible! (grr)
        Comparable[] b = new Comparable[a.length];
        sort(a,b,0,a.length-1);
    }

    private <T extends Comparable<? super T>> void sort(T[] a, T[] b, int low, int high) {
        if(low < high){
            int middle = (low+high) / 2;
            sort(a,b,low,middle);
            sort(a,b,middle+1,high);
            int s_high = middle+1;
            int s_low = low;
            for(int i = low; i <= high; i++){
                if((s_low <= middle) && ((s_high > high) || (a[s_low].compareTo(a[s_high]) < 0)))
                    b[i] = a[s_low++];
                else
                    b[i] = a[s_high++];
            }
            for(int i = low; i <= high; i++)
                a[i] = b[i];
        }
    }
}