【牛客网】直通bat-面试算法精品课_第2章 排序 2.6 快速排序练习题（JAVA版）

[1,2,3,5,2,3],6

[1,2,2,3,3,5]

import java.util.*;

public class QuickSort {
public int[] quickSort(int[] A, int n) {
// write code here
quicksort(A, 0, n-1);
return A;

}

public void quicksort(int[] A, int left, int right) {
if (left >= right) return;

int j = partition(A, left, right);
quicksort(A, left, j-1);
quicksort(A, j+1, right);

}

public int partition(int[] A, int left, int right) {
int len = right - left + 1;
Random rand = new Random();
int pivot = left + rand.nextInt(len);
exchange(A, pivot, right);
int index = left;

for(int k=left; k<left+(len-1); k++){
if (A[k] <= A[right]) {
exchange(A, index, k);
index ++;
}
}
exchange(A, index, right);
return index;

}

public void exchange(int[] A, int i, int j) {
int temp = A[i];
A[i] = A[j];
A[j] = temp;
}
}