How to add a value in an array to the values before and after it

Question

I am trying to turn an array of numbers into steps of the value of the Non-Zero integer element i.e

spread([0,0,n,0,0] returns => 
[0 + n-2, 0 + n-1, n, 0 +         


        

Answer 1

In three steps: 1. Explode the input array in an array of arrays, every containing single non-zero value. 2. Process every of those trivial cases separately. 3. Reduce them back into a single array.

(Not the optimal solution for sure, performance-wise).

const explode = arr => {
   const len = arr.length;

   return arr.map((val, index) => new Array(len)
      .fill(0)
      .map((x, j) => index === j ? val : 0)
   );
}

const pop = arr => {
   const nonZeroIndex = arr.findIndex(x => !!x);
   const nonZeroValue = arr.find(x => !!x);

   return nonZeroIndex !== -1 ?
      arr.map((x, i) => Math.max(0, nonZeroValue - Math.abs(i - nonZeroIndex))) :
      arr;
}

const sum2Arrays = (arrA, arrB) => arrA.map((x, i) => x + arrB[i]);
const sumArrays = arrs => arrs.reduce(sum2Arrays, Array(arrs[0].length).fill(0));

const spread = (arr) => sumArrays(explode(arr).map(pop));

console.log(spread([0, 0, 0, 0, 4, 0, 0, 3, 0]));