快速排序思路

快排的核心是partition函数。主要思路是，随机找一个值，然后遍历数组，大于该值的放在该值的右边，小于该值的放在该值的左侧。

algorithm quicksort(A, lo, hi) is
    if lo < hi then
        p := partition(A, lo, hi)
        quicksort(A, lo, p - 1)
        quicksort(A, p + 1, hi)

algorithm partition(A, lo, hi) is
    pivot := A[hi]
    i := lo
    for j := lo to hi do
        if A[j] < pivot then
            swap A[i] with A[j]
            i := i + 1
    swap A[i] with A[hi]
    return i

　　

public class QuickSort {
   public static void quickSort(int [] arr,int left,int right) {
      int pivot=0;
      if(left<right) {
         pivot=partition(arr,left,right);
         quickSort(arr,left,pivot-1);
         quickSort(arr,pivot+1,right);
      }
   }
   private static int partition(int[] arr,int left,int right) {
      int key=arr[left];
      while(left<right) {
         while(left<right && arr[right]>=key) {
            right--;
         }
         arr[left]=arr[right];
         while(left<right && arr[left]<=key) {
            left++;
         }
         arr[right]=arr[left];
      }
      arr[left]=key;
      return left;
   }

   public static void main(String[] args) {
      int arr[]= {65,58,95,10,57,62,13,106,78,23,85};
      System.out.println("排序前："+Arrays.toString(arr));
      quickSort(arr,0,arr.length-1);
      System.out.println("排序后："+Arrays.toString(arr));
   }
}

https://en.wikipedia.org/wiki/Quicksort