Then they just want to see if you know how to make a foreach loop. All I know about interview programmer tests, is that they want to see if you are familiar with basic functions and when to use them, for example:

• Loops
• Modulus
• etc.

Also, they have to be very clear about which "built-in" things they don't want then.

That was great way, but most interviewers request NOT to use in-built methods.

That was amazing!, using series formula for the sum n terms, as the nth sum is (n*(n+1))/2