codility test

min-positive-int.js

// given an array A of N integers, returns the smallest positive integer (greater than 0) that does not occur in A

function solution(A) {
  const sortedUnique = [...new Set([...A])]
   .filter((n) => (n > 0))
   .sort((a, b) => (a - b))
  if (sortedUnique.length === 0) return 1

  let invalidIdx = sortedUnique.findIndex((n, i) => n !== (i + 1))
  if (invalidIdx === -1) return sortedUnique[sortedUnique.length - 1] + 1
  if (invalidIdx === 0) return 1
  return sortedUnique[invalidIdx - 1] + 1
}