Omit Multiples (JS)

omit-multiples.js

const input = [1, 1, 1, 2, 3, 3, 5, 9]

const omitMultiples = list => {
  // Count the numbers in the list
  const counts = list
  .reduce((acc, el) => {
    const item = acc[el] || 0
    acc[el] = item + 1
    return acc
  }, {})
  
  // Add only numbers that occur once
  const results = []
  for (let c in counts) {
    const count = counts[c]
    if (count === 1) {
      results.push(c)
    }
  }
  return results
}

console.log(omitMultiples(input))