find sum in sorted list

by Arsen

HTML

<input type="number" id="inpSum" value="1634">
<button id="btnCalc">calculate</button>
<br>
<span id="resultMsg"></span>

CoffeeScript

a=[]
for i in [0..1000]
   a[i] = Math.floor 1 + Math.random() * 1000 

a.sort((a,b) -> a-b)

findpos = (arr, s, i1=0, i2=arr.length) ->
  curS = arr[i1] + arr[i2]
  switch
    when i1>=i2 then false 
    when s==curS then [arr[i1], arr[i2]]
    when s>=curS then findpos arr, s, i1 + 1, i2
    else findpos arr, s, i1, i2 - 1

elemById = (id) -> window.document.getElementById id

(elemById 'btnCalc')?.onclick = -> 
  sum = parseInt (elemById 'inpSum')?.value, 10
  (elemById 'resultMsg')?.innerText = findpos(a, sum)