Java实现的快速排序算法

import java.util.Arrays;
 import java.util.Random;
  
 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 <E extends Comparable<? super E>> int partition(E[] array, int begin, int end) {
         int index = begin + RND.nextInt(end - begin + 1);
         E pivot = array[index];
         swap(array, index, end);
         for (int i = index = begin; i < end; ++i) {
             if (array[i].compareTo(pivot) <= 0) {
                 swap(array, index++, i);
             }
         }
         swap(array, index, end);
         return (index);
     }
  
     private static <E extends Comparable<? super E>> void qsort(E[] array, int begin, int end) {
         if (end > begin) {
             int index = partition(array, begin, end);
             qsort(array, begin, index - 1);
             qsort(array, index + 1, end);
         }
     }
  
     public static <E extends Comparable<? super E>> void sort(E[] array) {
         qsort(array, 0, array.length - 1);
     }
  
     // Example uses
     public static void main(String[] args) {
         Integer[] l1 = { 5, 1024, 1, 88, 0, 1024 };
         System.out.println("l1  start:" + Arrays.toString(l1));
         QuickSort.sort(l1);
         System.out.println("l1 sorted:" + Arrays.toString(l1));
  
         String[] l2 = { "gamma", "beta", "alpha", "zoolander" };
         System.out.println("l2  start:" + Arrays.toString(l2));
         QuickSort.sort(l2);
         System.out.println("l2 sorted:" + Arrays.toString(l2));
     }
 }
 
Analogously to the Erlang solution above, a user-supplied {{Javadoc:SE|java/util|Comparator}} determines the partial ordering of array elements:
 
 import java.util.Comparator;
 import java.util.Random;
  
 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 <E> int partition(E[] array, int begin, int end, Comparator<? super E> 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 <E> void qsort(E[] array, int begin, int end, Comparator<? super E> 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 <E> void sort(E[] array, Comparator<? super E> cmp) {
         qsort(array, 0, array.length - 1, cmp);
     }
 }

标签： swap

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