Thread: Generating random numbers WITHOUT duplicates

To add to what sorenson said. A binary tree will allow you to do this quickly. Call rand in a loop and pass the output to your binary tree insert func which you have coded to reject duplicates. End the loop when the tree contains the right number of values. You could also use stl set or stl map to do this if that sounds like too much work for you.

If you can't be arsed to code a binary tree class then: if you know how many numbers you need, create an array of that size and fill it with 1, 2, 3... and swap random pairs a few thousand times (trivial for a PC). For more variety instead of having each slot one greater than the last make it a random amount bigger. Like:

Code:

void swap (int *one, int *two);

void main (void)
{
   int i;

   int num [20];
   int newNum = 1;

   int swapOne;
   int swapTwo;
   
   for (i = 0; i < 20; i++)
   {
      num [i] = newNum;
      newNum += (random (5));
   }

   for (i = 0; i < 9000; i++)
   {
      swapOne = random (20);

      do
      {
          swapTwo = random (20); 
      } while (swapTwo == swapOne);   // Avoid duplicates.

      swap (num + swapOne, num + swapTwo);   // Or use &num [swapOne], etc.
   }
}

void swap (int *one, int *two)
{
   int temp = *one;

   *one = *two;
   *two = temp;
}

If you have no random () function (like MSVC). The definition is as follows:

Code:

int random (int r)
{
   return (rand () % r);
}