对作为参数传递的数组进行混洗的函数

Question

我正在学校做一个项目，我想创建一个函数来对作为参数传递的数组进行混洗。 我试图创建一个，但它没有按我预期的那样工作......

在这段代码中，我试图复制传递数组的元素并在第二个数组中以随机顺序设置它们。 然后，在传递的数组中再次复制它们..

这是源代码：

void shufarray(int* array, int b)
{
    int hold[b];  
    int i,k;  
    int randV=0, randHold=0;
    srand(b);  
    for(i=0; i<b; ++i) {      
        hold[rand() % (b-1)] = array[i]; 
        k=0;
        do { 
            if(k==0) { 
                randHold = randV;
                k=-1;
            } //end if
            randV = rand()%(b-1);         
        } while(randHold != randV);//end of do\while stetment 
        hold[randV] = array[i];     
    } //end for  
    for(i=0;i<b;++i) {
        array[i]=hold[i]; 
    } //end for 
} //end shufarray()

这是输出：

hold[ 0 ] = 8
hold[ 1 ] = 11
hold[ 2 ] = 2
hold[ 3 ] = 15
hold[ 4 ] = 18
hold[ 5 ] = 10
hold[ 6 ] = 11
hold[ 7 ] = 17
hold[ 8 ] = 24
hold[ 9 ] = 21
hold[ 10 ] = 12
hold[ 11 ] = 2
hold[ 12 ] = 15
hold[ 13 ] = 9
hold[ 14 ] = 13
hold[ 15 ] = 1
hold[ 16 ] = 15
hold[ 17 ] = 1
hold[ 18 ] = 22
hold[ 19 ] = 11
hold[ 20 ] = 11
hold[ 21 ] = 18
hold[ 22 ] = 17
hold[ 23 ] = 4
hold[ 24 ] = 7
shuffled_hold[ 0 ] = 7
shuffled_hold[ 1 ] = 32561
shuffled_hold[ 2 ] = 22
shuffled_hold[ 3 ] = 0
shuffled_hold[ 4 ] = 18
shuffled_hold[ 5 ] = 8
shuffled_hold[ 6 ] = -632114865
shuffled_hold[ 7 ] = 32561
shuffled_hold[ 8 ] = -628693440
shuffled_hold[ 9 ] = 11
shuffled_hold[ 10 ] = 15
shuffled_hold[ 11 ] = 18
shuffled_hold[ 12 ] = 1
shuffled_hold[ 13 ] = 13
shuffled_hold[ 14 ] = 15
shuffled_hold[ 15 ] = 12
shuffled_hold[ 16 ] = 17
shuffled_hold[ 17 ] = 0
shuffled_hold[ 18 ] = 4
shuffled_hold[ 19 ] = 17
shuffled_hold[ 20 ] = 7
shuffled_hold[ 21 ] = 0
shuffled_hold[ 22 ] = -1
shuffled_hold[ 23 ] = 0
shuffled_hold[ 24 ] = 0

所以我试图了解这个操作的原理，任何人都可以帮我找出问题所在..谢谢。

Answer 1

问题

在前面的代码中，我认为解决方案是创建一个数组hold[]来保存从array[]随机复制的元素。 比将元素从hold[]再次复制回array[]问题是：

• hold[]未初始化

• 有时程序会覆盖已经覆盖的元素

• srand(b) 将始终根据长度给出相同的排列

解决方案

我根据评论中建议的参考修改了代码。

正确的做法是从最后一个元素array[n-1] ，将它与从整个数组（包括最后一个）中随机选择的元素交换。 现在考虑from 0 to n-2的数组（大小减 1），并重复该过程直到我们命中第一个元素。 详细算法如下：

  for i from n - 1 downto 1 do
       j = random integer with 0 <= j <= i
       exchange a[j] and a[i] .

编码

void shufarray(int* array, int b){
    int i,k=0;
    srand(time(NULL));//set the seed
    /* Starting from the last element and swap one by one.
     * NOTE: i > 0 it's because there's no need to run for the first element */
    for (i = b-1; i > 0; i--){
        int j = rand() % (i+1);
        //swap
        k =  array[i];
        array[i] = array[j];
        array[j] = k;
    }//end for
}//end shufarray()

输出

hold[ 0 ] = 8
hold[ 1 ] = 11
hold[ 2 ] = 2
hold[ 3 ] = 15
hold[ 4 ] = 18
hold[ 5 ] = 10
hold[ 6 ] = 11
hold[ 7 ] = 17
hold[ 8 ] = 24
hold[ 9 ] = 21
hold[ 10 ] = 12
hold[ 11 ] = 2
hold[ 12 ] = 15
hold[ 13 ] = 9
hold[ 14 ] = 13
hold[ 15 ] = 1
hold[ 16 ] = 15
hold[ 17 ] = 1
hold[ 18 ] = 22
hold[ 19 ] = 11
hold[ 20 ] = 11
hold[ 21 ] = 18
hold[ 22 ] = 17
hold[ 23 ] = 4
hold[ 24 ] = 7
shuffled_hold[ 0 ] = 24
shuffled_hold[ 1 ] = 9
shuffled_hold[ 2 ] = 8
shuffled_hold[ 3 ] = 1
shuffled_hold[ 4 ] = 15
shuffled_hold[ 5 ] = 11
shuffled_hold[ 6 ] = 11
shuffled_hold[ 7 ] = 21
shuffled_hold[ 8 ] = 17
shuffled_hold[ 9 ] = 7
shuffled_hold[ 10 ] = 11
shuffled_hold[ 11 ] = 11
shuffled_hold[ 12 ] = 18
shuffled_hold[ 13 ] = 10
shuffled_hold[ 14 ] = 1
shuffled_hold[ 15 ] = 15
shuffled_hold[ 16 ] = 13
shuffled_hold[ 17 ] = 2
shuffled_hold[ 18 ] = 18
shuffled_hold[ 19 ] = 4
shuffled_hold[ 20 ] = 17
shuffled_hold[ 21 ] = 2
shuffled_hold[ 22 ] = 12
shuffled_hold[ 23 ] = 15
shuffled_hold[ 24 ] = 22

参考资料： Fisher-Yates shuffle