two number sum

twoNumberSum.js

// O(n) time | O(n) space

function twoNumberSub(array, targetSum){
  let hashNumbers = {}
  for(const num of array){
    let potentialMatch = targetSum - num
    if(potentialMatch in hashNumbers){
      return [potentialMatch, num]
    }else{
      hashNumbers[num] = true // or whatever value you want, because we don't care about the value only key
    }
  }
  return []
}

// O(n log n) time | O(1) space
// if it's array try to sort it and have 2 pointes for more optimized solution
function twoNumberSum(array, targetSum){
  let leftIndices = 0
  let rightIndices = array.length - 1
  while (leftIndices < rightIndices){
    const currentSum = array[leftIndices] + array[rightIndices]
    if(currentSum === targetSum)
      return [array[leftIndices], array[rightIndices]]
    }else if (currentSum < targetSum){
     leftIndices++ 
    }else if(currentSum > targetSum){
     rightIndices--
    }
  return []
}


twoNumberSum([-4, -1,1,3,5,6,8,1], targetSum)