Function GPE(ByVal xMin As Long, ByVal xMax As Long, ByVal k As Byte, ByVal Tong As Long)
Dim Arr As Variant
Dim N As Long, i As Long, j As Byte, tmp As Long, kq As Long
N = xMax - xMin + 1
Arr = Tohop(N, k)
For i = LBound(Arr) To UBound(Arr)
tmp = 0
For j = 1 To N
If Mid(Arr(i), j, 1) = "1" Then tmp = tmp + xMin + j - 1
Next j
If tmp = Tong Then kq = kq + 1
Next i
GPE = kq
End Function
Private Function Tohop(ByVal N As Integer, ByVal k As Integer) As Variant
'tao to hop N chap k kha nang
If N = k Then Tohop = Array(String(k, "1")): Exit Function
Dim Arr As Variant, A As String, j As Long, p As Long, s As Long
ReDim Arr(1 To Application.Combin(N, k))
A = String(k, "1") & String(N - k, "0")
p = 1: Arr(p) = A
trolai:
j = InStrRev(A, "1")
Mid(A, j, 1) = "0"
Mid(A, j + 1, s + 1) = String(s + 1, "1")
s = 0: p = p + 1: Arr(p) = A
If InStr(j + 1, A, "0") = 0 Then
s = N - j
If s = k Then Tohop = Arr: Exit Function
Mid(A, j + 1, s) = String(s, "0")
End If
GoTo trolai
End Function
