快速排序

package com.alzhang.chapter03;  
  
import java.util.Comparator;  
import java.util.Random;  
  
@SuppressWarnings("unchecked")  
public class QuickSort {  
      
    public static final Random RND = new Random();  
  
    private static void swap(Object[] array, int i, int j) {  
        Object tmp = array[i];  
        array[i] = array[j];  
        array[j] = tmp;  
    }  
  
    private static int partition(Object[] array, int begin, int end, Comparator cmp) {  
        int index = begin + RND.nextInt(end - begin + 1);  
        Object pivot = array[index];  
        swap(array, index, end);  
        for (int i = index = begin; i < end; ++i) {  
            if (cmp.compare(array[i], pivot) <= 0) {  
                swap(array, index++, i);  
            }  
        }  
        swap(array, index, end);  
        return index;  
    }  
  
    private static void qsort(Object[] array, int begin, int end, Comparator cmp) {  
        if (end > begin) {  
            int index = partition(array, begin, end, cmp);  
            qsort(array, begin, index - 1, cmp);  
            qsort(array, index + 1, end, cmp);  
        }  
    }  
  
    public static void sort(Object[] array, Comparator cmp) {  
        qsort(array, 0, array.length - 1, cmp);  
    }  
  
}