Question

Given an integer n and an array a of length n, your task is to apply the following mutation to a:

Array a mutates into a new array b of length n.
For each i from 0 to n - 1, b[i] = a[i - 1] + a[i] + a[i + 1].
If some element in the sum a[i - 1] + a[i] + a[i + 1] does not exist, it should be set to 0. For example, b[0] should be equal to 0 + a[0] + a[1].
Example

For n = 5 and a = [4, 0, 1, -2, 3], the output should be mutateTheArray(n, a) = [4, 5, -1, 2, 1].

b[0] = 0 + a[0] + a[1] = 0 + 4 + 0 = 4
b[1] = a[0] + a[1] + a[2] = 4 + 0 + 1 = 5
b[2] = a[1] + a[2] + a[3] = 0 + 1 + (-2) = -1
b[3] = a[2] + a[3] + a[4] = 1 + (-2) + 3 = 2
b[4] = a[3] + a[4] + 0 = (-2) + 3 + 0 = 1
So, the resulting array after the mutation will be [4, 5, -1, 2, 1].

Answer 1

let a = [4, 0, 1, -2, 3];

let b = a.map( (e, i, arr) => (arr[i-1] || 0)+arr[i]+(arr[i+1] || 0) );

console.log(b);

Step-by-step explanation:

The map operator is excellent for this. The || 0 operator prevents the undefined out of bounds value from ruining the result.

BTW this solution is in javascript. Other languages will presumably require more code.