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;
  }
  }