This should be a fairly simple challenge.
For an array of numbers, generate an array where for every element all neighbouring elements are added to itself, and return the sum of that array.
Here is the transformation which occurs on the input array [1,2,3,4,5]
[1,2,3,4,5] => [1+2, 2+1+3, 3+2+4, 4+3+5, 5+4] => [3,6,9,12,9] => 39
0 => neighbours of item 0, including item 0
[1,2] => 1 + 2 => 3
1
[1,2,3] => 1 + 2 + 3 => 6
2
[2,3,4] => 2 + 3 + 4 => 9
3
[3,4,5] => 3 + 4 + 5 => 12
4
[4,5] => 4 + 5 => 9
3+6+9+12+9 => 39
Test cases
[] => 0 (or falsy)
[1] => 1
[1,4] => 10 (1+4 + 4+1)
[1,4,7] => 28
[1,4,7,10] => 55
[-1,-2,-3] => -14
[0.1,0.2,0.3] => 1.4
[1,-20,300,-4000,50000,-600000,7000000] => 12338842
Leaderboard
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