Re^2: Check randomly generated numbers have not been used before # Math!

[LanX]

> The odds of an actual collision for a 7-digit random number are so astronomically small that I quite frankly would not bother to check for it.

the odds for no collision are easily calculated:

> perl -e ' $x=1; $x*=(1e7-$_)/1e7 for 1..3723; print $x '
0.499919268547978

So the odds of a collision is already bigger than 50% after 3723 draws!¹

Actually there are already combinatorial formulas that avoids the loop completely.

For the interested readers:

• Birthday problem ²
• Conditional probability

¹) and bigger than 99% after 9600 draws!

²) which many of us should have encountered at school already ... :-/