快速排序

package leetcode.sort;

import java.util.Arrays;

/**
* QuickSort
* Created by blank on 2015-09-22 下午12:06.
*/
public class QuickSort {
static int[] arr = new int[20];

public static void main(String[] args) {
for (int i = 0; i < arr.length; i++) {
arr[i] = (int) (Math.random() * 200);
}
System.out.println(Arrays.toString(arr));
quickSort(0, arr.length - 1);
System.out.println(Arrays.toString(arr));

}

private static void quickSort(int left, int right) {
if (right - left < 1)
return;
swap(left, randint(left, right));//选取数组中随机一个元素作为划分元素
int tmp = arr[left];
int i = left;
int j = right + 1;
while (true) {
do i++; while (i <= right && arr[i] < tmp);//从左侧开始遍历,直到找到一个大于等于tmp的或者到达最右侧
do j--; while (arr[j] > tmp);//从右侧开始遍历,找到一个小于等于tmp的
if (i > j)//当交叉时 break
break;
swap(i, j);//不交叉则将左侧比tmp大的与右侧比tmp小的交换
}
swap(left, j);//循环终止时,交换a[left]和a[j]
quickSort(left, j - 1);//对左侧递归调用quickSort
quickSort(j + 1, right);//对右侧递归调用quickSort
}

private static void swap(int x, int y) {
int tmp = arr[x];
arr[x] = arr[y];
arr[y] = tmp;
}

private static int randint(int a, int b) {
//产生a与b之间的随机数
return a + (int) (Math.random() * 100) % (b - a + 1);
}
}