JavaScript algorithm problem (i) && array reduce use

Refer to Array.reduce Usage

1. Write the Getmissingelement function to return the missing element in the given array (the element in the array is 0~9, only one is missing).

Example:

Getmissingelement ([0, 5, 1, 3, 2, 9, 7, 6, 4]) //returns 8

Getmissingelement ([9, 2, 4, 5, 7, 0, 8, 6, 1]) //returns 3

Soluction:

function Getmissingelement (superimportantarray) {  return superimportantarray.reduce (function (sum,i) {return SUM-I;},45)}

2.Write a function that flattens an array of the array objects into a flat array. Your function must only does one level of flattening.

Exmaple:

Flatten ([123])//= [+/-]

Flatten ([[1,2,3],["A", "B", "C"],[1,2,3]])//=>[1,2,3, "A", "B", "C", [+])

Flatten ([[[[[I]]])//= [[[+]]

Soluction:

var flatten = function (array) {   return array.reduce (function (b) {       return a.concat (b);   },[])}

　　

JavaScript algorithm problem (i) && array reduce use