Code golf: combining multiple sorted lists into a single sorted list

Question

Implement an algorithm to merge an arbitrary number of sorted lists into one sorted list. The aim is to create the smallest working programme, in whatever language you like.

Answer 1

VB is usually not the language of choice for code golf, but here goes anyway.

The setup -

        Dim m1 As List(Of Integer) = New List(Of Integer)
        Dim m2 As List(Of Integer) = New List(Of Integer)
        Dim m3 As List(Of Integer) = New List(Of Integer)
        Dim m4 As List(Of Integer) = New List(Of Integer)

        m1.Add(1)
        m1.Add(2)
        m1.Add(3)

        m2.Add(4)
        m2.Add(5)
        m2.Add(6)

        m3.Add(7)
        m3.Add(8)
        m3.Add(9)

        Dim m5 As List(Of List(Of Integer)) = New List(Of List(Of Integer))
        m5.Add(m1)
        m5.Add(m2)
        m5.Add(m3)

An attempt in VB.NET (without sort)

        While m5.Count > 0
            Dim idx As Integer = 0
            Dim min As Integer = Integer.MaxValue
            For k As Integer = 0 To m5.Count - 1
                If m5(k)(0) < min Then min = m5(k)(0) : idx = k
            Next
            m4.Add(min) : m5(idx).RemoveAt(0)
            If m5(idx).Count = 0 Then m5.RemoveAt(idx)
        End While

Another VB.NET attempt (with an allowed sort)

    Private Function Comp(ByVal l1 As List(Of Integer), ByVal l2 As List(Of Integer)) As Integer
        Return l1(0).CompareTo(l2(0))
    End Function
    .
    .
    .
    While m5.Count > 0
        m5.Sort(AddressOf Comp)
        m4.Add(m5(0)(0)) : m5(0).RemoveAt(0)
        If m5(0).Count = 0 Then m5.RemoveAt(0)
    End While

The entire program -

        Dim rand As New Random
        Dim m1 As List(Of Integer) = New List(Of Integer)
        Dim m2 As List(Of Integer) = New List(Of Integer)
        Dim m3 As List(Of Integer) = New List(Of Integer)
        Dim m4 As List(Of Integer) = New List(Of Integer)
        Dim m5 As List(Of List(Of Integer)) = New List(Of List(Of Integer))
        m5.Add(m1)
        m5.Add(m2)
        m5.Add(m3)

        For Each d As List(Of Integer) In m5
            For i As Integer = 0 To 100000
                d.Add(rand.Next())
            Next
            d.Sort()
        Next

        Dim sw As New Stopwatch
        sw.Start()
        While m5.Count > 0
            Dim idx As Integer = 0
            Dim min As Integer = Integer.MaxValue
            For k As Integer = 0 To m5.Count - 1
                If m5(k)(0) < min Then min = m5(k)(0) : idx = k
            Next
            m4.Add(min) : m5(idx).RemoveAt(0)
            If m5(idx).Count = 0 Then m5.RemoveAt(idx)
        End While
        sw.Stop()

        'Dim sw As New Stopwatch
        'sw.Start()
        'While m5.Count > 0
        '    m5.Sort(AddressOf Comp)
        '    m4.Add(m5(0)(0)) : m5(0).RemoveAt(0)
        '    If m5(0).Count = 0 Then m5.RemoveAt(0)
        'End While
        'sw.Stop()

        Console.WriteLine(sw.Elapsed)
        Console.ReadLine()