Ugly structures that don't map to clear concepts are worse than any special case. Padding array makes you go "wtf is that?" I would rather see something like

Ugly structures that don't map to clear concepts are worse than any special case. Padding array makes you go "wtf is that?" I would rather see something like this: (i > 0 ? input[i-1] : 0) + (i < input.size - 1 ? input[i+1] : 0) which clearly maps to "if there is a left neighbor, add it; if there is a right neighbor, add it; return the sum."