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快速排序(Quicksort)，因其排序之快而得名，虽然Ta的平均时间复杂度也是o(nlgn)，但是从后续仿真结果看，TA要比归并排序和堆排序都要快。
快速排序也用到了分治思想。
（一）算法实现
1 protected void quicksort(int[] array, int first, int last) { 2 3 int pivot = array[first]; 4 int i = first; 5 int j = last - 1; 6 boolean serachBig = true; 7 while (i < j) { 8 if (serachBig) { 9 if (array[j] < pivot) { 10 array[i] = array[j]; 11 i++; 12 serachBig = false; 13 } else { 14 j--; 15 } 16 } else { 17 if (array[i] > pivot) { 18 array[j] = array[i]; 19 j--; 20 serachBig = true; 21 } else { 22 i++; 23 } 24 } 25 } 26 array[i] = pivot; 27 28 if (i - first > 1) { 29 quicksort(array, first, i); 30 } 31 if (last - i > 2) { 32 quicksort(array, i + 1, last); 33 } 34 }
1）快速排序的平均时间复杂度也是o(nlgn)
2）快速排序属于原地排序
（二）仿真结果
**************************************************
Number to Sort is:2500
Array to sort is:{378132,303655,213274,506865,348563,122685,857064,624884,376943,281167...}
Cost time of 【QuickSort】 is(milliseconds):0
Sort result of 【QuickSort】:{93,862,991,1285,2737,2938,3119,3372,3933,4647...}
**************************************************
Number to Sort is:25000
Array to sort is:{737677,533972,6498,772664,516805,635063,278963,284929,577222,593745...}
Cost time of 【QuickSort】 is(milliseconds):2
Sort result of 【QuickSort】:{1,247,270,375,386,428,431,515,588,623...}
**************************************************
Number to Sort is:250000
Array to sort is:{481818,650680,957183,733420,611440,739781,495686,560166,942993,492550...}
Cost time of 【QuickSort】 is(milliseconds):23
Sort result of 【QuickSort】:{0,6,10,17,20,22,23,26,32,37...}
相关代码：
1 package com.cnblogs.riyueshiwang.sort; 2 3 import java.util.Arrays; 4 5 public class QuickSort extends abstractSort { 6 7 @Override 8 protected void sort(int[] toSort) { 9 quicksort(toSort, 0, toSort.length); 10 } 11 12 protected void quicksort(int[] array, int first, int last) { 13 14 int pivot = array[first]; 15 int i = first; 16 int j = last - 1; 17 boolean serachBig = true; 18 while (i < j) { 19 if (serachBig) { 20 if (array[j] < pivot) { 21 array[i] = array[j]; 22 i++; 23 serachBig = false; 24 } else { 25 j--; 26 } 27 } else { 28 if (array[i] > pivot) { 29 array[j] = array[i]; 30 j--; 31 serachBig = true; 32 } else { 33 i++; 34 } 35 } 36 } 37 array[i] = pivot; 38 39 if (i - first > 1) { 40 quicksort(array, first, i); 41 } 42 if (last - i > 2) { 43 quicksort(array, i + 1, last); 44 } 45 } 46 47 public static void main(String[] args) { 48 for (int j = 0, n = 2500; j < 3; j++, n = n * 10) { 49 System.out 50 .println("**************************************************"); 51 System.out.println("Number to Sort is:" + n); 52 int[] array = CommonUtils.getRandomIntArray(n, 1000000); 53 System.out.print("Array to sort is:"); 54 CommonUtils.printIntArray(array); 55 56 int[] array1 = Arrays.copyOf(array, n); 57 new QuickSort().sortAndprint(array1); 58 } 59 } 60 61 }
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原文地址：http://www.cnblogs.com/riyueshiwang/p/4591254.html
