面试常用算法之排序

Posted 2022-08-24 pipicai96

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;