无重复的随机数组生成

If you want to generate a random array without duplicates the rand() method is not working at all.

Let say you want to generate an array of 1000 numbers. In the best case let say you generated the first 999 numbers without duplicates and last think to do is generating the last number. The probability of getting that number is 1/1000 so this is almost going to take forever to get generated. In practice only 10 numbers makes a big trouble.

The best method is to generate all your numbers by incrementation (or strictly monotonic sequence) is shuffle them. In this case there will be no duplicates

Here is an exemple on how to do it with 10 numbers. Even with 1000 numbers it's working.

Note: Suffle function from Jhon Leehey's answer.

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

void shuffle(int *arr, size_t n)
{
    if (n > 1) 
    {
        size_t i;
        srand(time(NULL));
        for (i = 0; i < n - 1; i++) 
        {
          size_t j = i + rand() / (RAND_MAX / (n - i) + 1);
          int t = arr[j];
          arr[j] = arr[i];
          arr[i] = t;
        }
    }
}

int main()
{
    int i;
    int arr[10];
    for (i=0; i<10; i++){
        arr[i] = i;
    }
    shuffle(arr, 10);
    for (i=0; i<10; i++){
        printf("%d ", arr[i]);
    }
}

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