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.

Given an integer array nums, which may or may not be sorted, the goal is find the smallest missing positive integer.

For example:
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

Raku

<lang perl6>say $_, " ==> ", 1 + .max max 1 for [ 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], []</lang>

Output:

[1 2 0] ==> 3
[3 4 -1 1] ==> 5
[7 8 9 11 12] ==> 13
[1 2 3 4 5] ==> 6
[-6 -5 -2 -1] ==> 1
[5 -5] ==> 6
[-2] ==> 1
[1] ==> 2
[] ==> 1

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