Largest level of tree

largest-level-of-tree.js

var findLargestLevel = (node) => {
  // make levelObj as closure var 
  const levelObj = {};
  // inner function takes in node and level
  const innerFunc = (node, level) => {
    // if levelObj doesn't have property at this level 
    if (levelObj[level] === undefined) {
      // create a new value, with the node inside an array
      levelObj[level] = [node];
    // otherwise
    } else {
      // concat the current node into the array
      levelObj[level] = levelObj[level].concat(node);
    }
    // if left node != undefined
    if (node.left !== undefined) {
      // recurse into the left node, with level incremented
      innerFunc(node.left, level + 1);
    }
    // if right node != undefined
    if (node.right !== undefined) {
      // recurse into the right node, with level incrementd
      innerFunc(node.right, level + 1);
    }
  }
  // initial invocation with root and level as 0
  innerFunc(node, 0);
  // make largestLevel var as [value, level]
  let largestLevel = [0, 0];
  // for level in levelObj
  for (level in levelObj) {
    // reduce each level's value (array) into sum
    if (levelObj[level].length === 1) {
      var sum = levelObj[level][0].value;
    } else {
      var sum = levelObj[level].reduce((a, b) => {
        return a.value + b.value;
      });
    }
    // if the reduced sum is greater than largestLevel[0] value, 
    if (sum > largestLevel[0]) {
      // update the largestLevel array
      largestLevel = [sum, Number(level)];
    }
  }
  // return the largestLevel's level (second index)
  return largestLevel[1];
};