nest-list-weighted-sum.js

/*
Given a nested list of integers, return the sum of all integers in the list weighted by their depth.

Each element is either an integer, or a list -- whose elements may also be integers or other lists.

Example 1:
Given the list [[1,1],2,[1,1]], return 10. (four 1's at depth 2, one 2 at depth 1)

Example 2:
Given the list [1,[4,[6]]], return 27. (one 1 at depth 1, one 4 at depth 2, and one 6 at depth 3; 1 + 4*2 + 6*3 = 27)
*/

var depthSum = function(nestedList, depth) {

  var result = 0;
  depth = depth || 1;

  for (let i = 0; i < nestedList.length; i++) {
    if (Array.isArray(nestedList[i])) {
      result += depthSum(nestedList[i], depth + 1);
    } else {
      result += nestedList[i] * depth;
    }
  }
  return result;
};