MissingInteger

Problem: Write a function that, given an array A of N integers, returns the smallest positive integer (greater than 0) that does not occur in A.

Solution:

If there is no array or the array has no length, we'll return 0.

if (!A || !A.length) return 0

Then I sorted the array from smallest to largest.

A.sort((a, b) => a - b)

Then I created a new Set and add each positive integer to the Set so I can have a collection without duplicate numbers.

let p = new Set()
A.forEach(function (value) {
  if (value > 0) p.add(value)
})

Then if the set doesn't have a size, I return 1 since it is the first postive integer missing.

if (!p.size) return 1

I then loop through the set (starting with 1 to the size of the set) checking if the index number exists in the set. If it doesn't, I return that number as the smallest positive integer. If the loop completes without returning anything, I then return the set size plus one as the smallest integer.

for (i = 1; i <= p.size; i++) {
  if (!p.has(i)) return i
}

return p.size + 1

Here is the completed function that satisfied the solution scoring 100%.

function solution(A) {
  if (!A || !A.length) return 0

  A.sort((a, b) => a - b)

  let p = new Set()
  A.forEach(function (value) {
    if (value > 0) p.add(value)
  })

  if (!p.size) return 1

  for (i = 1; i <= p.size; i++) {
    if (!p.has(i)) return i
  }

  return p.size + 1
}

Again, I'm sure there are many other possibilities but this worked for me.