Suppose you want to make a random 9 digit number, using every number from 1 to 9 exactly once. You have a process called random(top) that gives a random number up to top (if top was 5, it would give random numbers from 1 to 5)

a) How could you do this?

b) If top couldn't be more than 9, how could you do this using random(top) only 9 times (or less)?

for i = 9 down to 1,
set array[i] to i
for i = 9 down to 1,
swap array[i] with array[random(i)]

Posted by Federico Kereki on 2003-07-14 15:35:14