The third hardest challenge listed in the “easy” section of Coderbyte.

scaleBalancing.js

function scaleBalancing(plates, weights) {

  weights.sort((a, b) => a - b)
  
  let [a, b] = plates
  
  if (a === b) {
    
    return 'already balanced'
  }
  
  let diff = Math.abs(a - b)
  
  if (weights.includes(diff)) {
    
    return '' + diff
  }
  
  for (let i = 0; i < weights.length; i++) {

    let copy = [...weights]
    copy.splice(i, 1)

    let solution = copy.indexOf(diff - weights[i])

    if (solution > -1) {

      return [weights[i], weights[solution + 1]].toString()
    }
  }
  
  let biggest = Math.max(a, b)
  let smallest = Math.min(a, b)
  
  for (let i = 0; i < weights.length; i++) {
  
    let sum = biggest + weights[i]
    
    let copy = [...weights]
    copy.splice(i, 1)
    
    let solution = copy.indexOf(sum - smallest)
    
    if (solution > -1) {
      
      return [weights[i], weights[solution + 1]].toString()
    }
  }
  
  return 'impossible'
}