public static void main(String[] args) {
    
    

        int[] arr = {
    
    5, 6, 4, 3, 2, 1};

        sort(arr, 0, arr.length - 1);

        for (int i = 0; i < arr.length; i++) {
    
    
            System.out.print(arr[i] + " ");
        }

    }

    private static void sort(int[] arr, int p, int r) {
    
    
        if (p < r) {
    
    
            int q = partition1(arr, p, r);
            sort(arr, p, q - 1);
            sort(arr, q + 1, r);
        }
    }
//双向
    public static int partition1(int[] arr, int p, int r) {
    
    
        int pivot = arr[p];
        int sp = p + 1;
        int big = r;
        while (sp <= big) {
    
    
            while (sp <= big && arr[sp] <= pivot) {
    
    
                sp++;
            }
            while (sp <= big && arr[big] > pivot) {
    
    
                big--;
            }
            if (sp < big) {
    
    
                int temp = arr[big];
                arr[big] = arr[sp];
                arr[sp] = temp;
            }
        }
        int temp = arr[p];
        arr[p] = arr[big];
        arr[big] = temp;

        return big;

    }