Question: Define a function 'gcd' that returns the greatest common divisor of two or more integers, as an integer.
More Information:
https://en.wikipedia.org/wiki/Greatest_common_divisor
q)gcd 10 5 15
5
q)gcd 5*til 100000
5
q)gcd 1+5*til 100000
1
######## solution.q ########
gcd:{$[y=0;x;.z.s[y;x mod y]]}/
Explanation: To compute GCD between two numbers, get the remainder between the first and second number. If it is 0, then the greatest common divisor is the second number, otherwise get the remainder again between the second number and the new remainder. Keep doing this recursively until your remainder is 0. To apply this over a list, use the over adverb '/'.