无重复数的随机数组

Question

So what I am trying to do is create a random array of 5 elements, those elements should be filled with numbers from 1 to 6 and they shall not repeat, I can't tell where my logic is wrong.

void genNumber(int vet[]){
   int max, i, j, atual;
   srand(time(NULL));

   max = 7;
   for (i=0;i<5;i++){
      vet[i] = rand() % max;
      while(vet[i] == 0){
         vet[i] = rand() % max;
      }

      for(j=0;j<i;j++){
         atual = vet[j];
         while((vet[i] == atual)||(vet[i] == 0)){
            vet[i] = rand() % max;
            atual = vet[j];
         }
      }
   }
}

Update: Fixed

void genNumber(int vet[]){
int max, i, j;
srand(time(NULL));

max = 7;
for (i=0;i<5;i++){
    vet[i] = rand() % (max-1) + 1;

    for(j=0;j<i;j++){
        while(vet[j] == vet[i]){
            vet[i] = rand() % (max-1) + 1;
            j = 0;
        }
    }
}
}

Answer 1

The logical flaw is in the way you produce a new random number when a duplicate is found.

Imagine you already have vel = {1,2,0,0,0,...} and are trying to find a number for vel[2] . If you randomly draw a 2 , you'll find it's already there and draw again. But if you draw a 1 this time you won't notice, because you only compare to the last value seen, 2 in the example. So you'd get vel = {1,2,1,...} .

"Solution": Every time you draw a new random number you have to compare it against all numbers already in the list.

Another way of solving this is the one I tried to outline in the comments: You have to keep the information about which numbers are still valid for a draw somewhere. You can either use the "output" array for that as you're doing now, or you can use another store from which you "remove" an entry once it was drawn.

Answer 2

when generating a random number,you have to check if it is found in the array,so iterate over the array and check.if the number is found,generate another random number and check,until the new number is not found in the array.after that assign it.and repeat.

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

int check(int vet[],size_t size,int val);

void genNumber(int vet[],size_t size);

int main(void)
{
    srand(time(NULL));

    int vet[5];

    size_t size = 5;

    genNumber(vet,size);

    for( size_t n = 0 ; n < size ; n++ )
    {
        printf("%d ",vet[n]);
    }
}

void genNumber(int vet[],size_t size)
{
    int num = rand() % 6 + 1;

    vet[0] = num;

    for( size_t n = 1 ; n < size ; n++ )
    {
        num = rand() % 6 + 1;
        while( 1 )
        {
            if( check(vet,n,num) )
            {
                num = rand() % 6 + 1;
            }
            else
            {
                vet[n] = num;
                break;
            }
        }
    }
}

int check(int vet[],size_t size,int val)
{
    for( size_t n = 0 ; n < size ; n++ )
    {
        if( vet[n] == val )
        {
            return 1;//FOUND
        }
    }
    return 0;//NOT FOUND
}

Answer 3

As an alternative you can fill an array with a value from 1 to 6. Afterwards you can shuffle the array at random indicies.

#define MAX 6

void swap (int *a, int *b) {
  int temp = *a;
  *a = *b;
  *b = temp;
}

void genNumber(int *vet) {
  int i;

  for(i=0;i<MAX;i++) {
    vet[i] = i+1;
  }

  for(i = MAX-1;i > 0;i--) {
    // Pick a random index from 0 to i
    int j = rand() % (i+1);
    // Swap vet[i] with the element at random index
    swap(&vet[i], &vet[j]);
  }
}

Also you shouldn't call srand(time(NULL)); inside of the genNumber function if you intend to call it more than once, becaues otherwise it will give you the same numbers if you call it more than once a second.

Afterwards just use the first five elements from the array. So you would call it like this from main

int vet[MAX] = {0};
srand(time(NULL));
genNumber(vet);
for(i=0;i<5;i++) {
  printf("after num %d\n", vet[i]);
}