Find first missing positive

Find first missing positive is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

Let given an unsorted integer array nums. The goal is find the smallest missing positive integer.
nums = [1,2,0], [3,4,-1,1], [7,8,9,11,12]
output = 3, 2, 1

Julia

<lang julia> for array in [[1,2,0], [3,4,-1,1], [7,8,9,11,12], [-5, -2, -6, -1]]

   a = sort(array)
   x = findfirst(i -> a[i] > -1 && a[i + 1] - a[i] > 1, 1:length(a)-1)
   println("$array  =>  ", x != nothing ? a[x] + 1 : a[end] > -1 ? a[end] + 1 : "None")

end

</lang>

Output:

[1, 2, 0]  =>  3
[3, 4, -1, 1]  =>  2
[7, 8, 9, 11, 12]  =>  10
[-6, -5, -2, -1]  =>  None

Ring

<lang ring> nums = [[1,2,0],[3,4,-1,1],[7,8,9,11,12]] numnr = list(3) numnr[1] = "[1,2,0]" numnr[2] = "[3,4,-1,1]" numnr[3] = "[7,8,9,11,12]"

for n = 1 to len(nums)

   sortNums = sort(nums[n])
   ln = len(sortNums)
   num = sortNums[ln]   
   for m = 1 to num + 1
       ind = find(nums[n],m)
       if ind < 1
          see "the smallest missing positive integer for " + numnr[n] + ": " + m + nl
          exit
       ok
   next

next </lang>

Output:

the smallest missing positive integer for [1,2,0]: 3
the smallest missing positive integer for [3,4,-1,1]: 2
the smallest missing positive integer for [7,8,9,11,12]: 1

Wren

Library: Wren-sort

<lang ecmascript>import "/sort" for Sort

var firstMissingPositive = Fn.new { |a|

   var b = a.where { |i| i > 0 }.toList
   Sort.insertion(b)
   if (b.isEmpty || b[0] > 1) return 1
   var i = 1
   while (i < b.count) {
       if (b[i] - b[i-1] > 1) return b[i-1] + 1
       i = i + 1    
   }
   return b[-1] + 1

}

System.print("The first missing positive integers for the following arrays are:\n") var aa = [

   [ 1, 2, 0], [3, 4, -1, 1], [7, 8, 9, 11, 12], [1, 2, 3, 4, 5],
   [-6, -5, -2, -1], [5, -5], [-2], [1], []

] for (a in aa) System.print("%(a) -> %(firstMissingPositive.call(a))")</lang>

Output:

The first missing positive integers for the following arrays are:

[1, 2, 0] -> 3
[3, 4, -1, 1] -> 2
[7, 8, 9, 11, 12] -> 1
[1, 2, 3, 4, 5] -> 6
[-6, -5, -2, -1] -> 1
[5, -5] -> 1
[-2] -> 1
[1] -> 2
[] -> 1