#Japt, 7 bytes

Man, I fought with the wrong Japt method for far too long trying to get it to work for the [1], 3 test case in a reasonable amount of bytes!

VÆëVX x

Try it

##Explanation Implicit input of array U and integer V.

VÆ

Generate an array of integers from 0 to V-1 and pass each through a function with X being the current element.

ëVX

Grab every Vth element of U, beginning at index X.

x

Reduce that array by addition.

Japt, 7 bytes

Man, I fought with the wrong Japt method for far too long trying to get it to work for the [1], 3 test case in a reasonable amount of bytes!

VÆëVX x

Try it

Explanation

Implicit input of array U and integer V.

VÆ

Generate an array of integers from 0 to V-1 and pass each through a function with X being the current element.

ëVX

Grab every Vth element of U, beginning at index X.

x

Reduce that array by addition.

#Japt, 7 bytes

Man, I fought with the wrong method for far too long trying to get it to work for the [1], 3 test case in a reasonable amount of bytes!

Takes input in reverse order (although doing so doesn't save any bytes).

ÆVëUX x

Try it

##Explanation Implicit input of integer U and array V.

Æ

Generate an array of integers from 0 to U-1 and pass each through a function with X being the current element.

VëUX

Grab every Uth element of V, beginning at index X.

x

Reduce that array by addition.

#Japt, 7 bytes

Man, I fought with the wrong Japt method for far too long trying to get it to work for the [1], 3 test case in a reasonable amount of bytes!

VÆëVX x

Try it

##Explanation Implicit input of array U and integer V.

VÆ

Generate an array of integers from 0 to V-1 and pass each through a function with X being the current element.

ëVX

Grab every Vth element of U, beginning at index X.

x

Reduce that array by addition.

#Japt, 7 bytes

Man, I fought with the wrong method for far too long, trying to get this to work with the [1], 3 test case in a reasonable amount of bytes!

Takes input in reverse order (although doing so doesn't save any bytes).

ÆVëUX x

Try it

##Explanation Implicit input of integer U and array V.

Æ

Generate an array of integers from 0 to U-1 and pass each through a function with X being the current element.

VëUX

Grab every Uth element of V, beginning at index X.

x

Reduce that array by addition.

#Japt, 7 bytes

Man, I fought with the wrong method for far too long trying to get it to work for the [1], 3 test case in a reasonable amount of bytes!

Takes input in reverse order (although doing so doesn't save any bytes).

ÆVëUX x

Try it

##Explanation Implicit input of integer U and array V.

Æ

Generate an array of integers from 0 to U-1 and pass each through a function with X being the current element.

VëUX

Grab every Uth element of V, beginning at index X.

x

Reduce that array by addition.