Optimising JavaScript for an exercise on Codewars

Question

I'm currently working on my JavaScript by doing exercises on Codewars.com. I've been doing OK but I've come across this question and I can't figure out a way to optimize it. Here is the question:

Sum of Pairs

Given a list of integers and a single sum value, return the first two values (parse from the left please) in order of appearance that add up to form the sum.

sum_pairs([0, 0, -2, 3], 2)
#  there are no pairs of values that can be added to produce 2.
== None/nil/undefined (Based on the language)

sum_pairs([10, 5, 2, 3, 7, 5],         10)
#              ^-----------^   5 + 5 = 10, indices: 1, 5
#                    ^--^      3 + 7 = 10, indices: 3, 4 *
#  * entire pair is earlier, and therefore is the correct answer
== [3, 7]

NOTE: There will also be lists tested of lengths upwards of 10,000,000 elements. Be sure your code doesn't time out.

It's simple enough and my solution works, but times out after 12 seconds on the 10,000,000 elements test.

My solution:

function sum_pairs(numArray, num){
  var nums = numArray;
  var sum = num;
  var resultsArray = [];
  var result;

  for(var i = 0; i < nums.length; i++){
    for(var j = i+1; j < nums.length; j++){
      if(nums[i] + nums[j] == sum){
        resultsArray.push({resArray: [nums[i],nums[j]], weight: j});
      }
    }
  }

  if(resultsArray.length != 0){
  var result = resultsArray.pop();
    for(var i = 0; i < resultsArray.length; i++){
      if(result.weight > resultsArray[i].weight){
        result = resultsArray[i];
      }
    }
    result = result.resArray;
  }

  return result;

}

Question:

How to optimize this code so that it doesn't time out. I'm just a beginner programming wise and I'm unsure what part(s) of my solution causes slowdown. I'm about to read up on Big O notation now, any other resources for learning about code optimization?

Good question, but this is probably better suited for codereview.stackexchange.com — Marvin
– Marvin, Commented May 8, 2017 at 15:29

emed · Accepted Answer · 2017-05-08 17:24:07Z

2

For example [a,b,c,d,e]

Instead of taking a and testing against the right side (b,c,d,e)

[a,b,c,d,e]
 i j j j j
   i j j j
     i j j
       i j

Start at b and test against the left side (a)

[a,b,c,d,e]
 j i
 j j i
 j j j i
 j j j j i

This way the first match you find is the one you want, and you can return without having to loop through the whole array.

answered May 8, 2017 at 17:24

emed

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4 Comments

user2831946 Over a year ago

Changed the solution to this: function sum_pairs(numArray, num){ }

user2831946 Over a year ago

Sorry my formating was off and then I ran out of editing time >< My code looks like this now:

function sum_pairs(numArray, num){  var nums = numArray;  var sum = num;  var resultsArray = [];   for(var i = 0; i < nums.length; i++){     for(var j = 0; j < i; j++){        if(nums[i] + nums[j] == sum){           return [nums[j], nums[i]];        }      }   } }

Still doesn't run fast enough!! Thanks for the suggestion though. Pissed off with this question now but I really want to solve it!

user2831946 Over a year ago

Very new to stack overflow, struggling with the formatting in the comments. Seems to be handled very differently... Have to look up how to add new lines...

emed Over a year ago

@user2831946 I dont think you can add new lines in comments, and too bad the change wasn't enough :S

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