Random array generation with no duplicates

Question

I am trying to create something that generates a random array with no duplicate values. I\'ve already looked at other answers but none seem to help me understand. I cannot t

Answer 1

If you want to pseudo-randomly traverse a large space without maintaining visited indices, you should look at this project I contributed to years ago for the basic technique. http://packetfactory.openwall.net/projects/ipspace/index.html

You should be able to adapt it to your purposes, source is at the bottom of the page.

Answer 2

You start off filling a container with consecutive elements beginning at 0

std::iota(begin(vec), end(vec), 0);

then you get yourself a decent random number generator and seed it properly

std::mt19937 rng(std::random_device{}());

finally you shuffle the elements using the rng

std::shuffle(begin(vec), end(vec), rng);

live on coliru

---

On some implementations random_device doesn’t work properly (most notably gcc on windows) and you have to use an alternative seed, i.e. the current time → chrono.

Answer 3

srand(time(NULL));
const int N = 4;
int numbers [N];

bool isAlreadyAdded(int value, int index)
{
     for( int i = 0; i < index; i ++)
          if( numbers[i] == value)
              return true;
     return false;
}
for (int x=0; x!=N;x++)
{
    int tmp = 1 + (rand() % N) ;
    while( x !=0 && isAlreadyAdded(tmp, x))
           tmp = 1 + (rand() % N) ;

    numbers[x] = tmp;
    printf("%d ", numbers[x]);
}

It's just a way. it should work, of course there are better ways