常用算法之排序(3)

快速排序

``` package algorithm.sort;

/**

  • 快速排序

  • 思想:类似于归并排序,但是不同于归并排序每次排序寻找一次子数组中点的是,寻找一个更恰当的分区点

  • @Author 28370

  • @Date 2019-5-13
    **/
    public class QuickSort {
    public static void main(String[] args) {
    int[] a= {1,7,4,8,5,3,9,2};
    quickSort(a);
    for (int i = 0; i < a.length; i++) {
    System.out.println(a[i]);

     }
    

    }

    public static void quickSort(int[] a){
    quickSortInternally(a, 0, a.length-1);
    }

    private static void quickSortInternally(int[] a, int p, int r) {
    if(p >= r){
    return ;
    }
    int q = partition(a, p, r);
    quickSortInternally(a, p, q-1);
    quickSortInternally(a, q+1, r);
    }

    //获取分区点
    private static int partition(int[] a, int p, int r) {
    int pivot = a[r];
    System.out.println(pivot);
    int i = p;
    for (int j = p; j < r; ++j) {
    System.out.println("j="+j+",a[j]="+a[j]);
    System.out.println("i="+i+",a[i]="+a[i]);
    if(a[j] < pivot){
    if(i == j){
    ++i;
    }else{
    int temp = a[i];
    a[i++] = a[j];
    a[j] = temp;
    }
    }
    }
    int tmp = a[i];
    a[i] = a[r];
    a[r] = tmp;
    System.out.println("i="+i);
    String str ="";
    for (int j = 0; j < a.length; j++) {
    str+=a[j];
    }
    System.out.println(str);
    return i;
    }
    }

posted @ 2019-08-25 12:47  AaronPi  阅读(197)  评论(0编辑  收藏  举报