N-queens problem: Difference between revisions
→{{header|FreeBASIC}}
Line 4,768:
A 13 x 13 board has 73712 solutions
A 14 x 14 board has 365596 solutions</pre>
=== Alternate version : recursive ===
<lang freebasic>Sub aux(n As Integer, i As Integer, a() As Integer, _
u() As Integer, v() As Integer, ByRef m As LongInt)
Dim As Integer j, k, p, q
If i > n Then
m += 1
For k = 1 To n : Print a(k); : Next : Print
Else
For j = i To n
k = a(j)
p = i - k + n
q = i + k - 1
If u(p) And v(q) Then
u(p) = 0 : v(q) = 0
a(j) = a(i) : a(i) = k
aux(n, i + 1, a(), u(), v(), m)
u(p) = 1 : v(q) = 1
a(i) = a(j) : a(j) = k
End If
Next
End If
End Sub
Dim As Integer n, i
Dim m As LongInt = 1
If Command(1) <> "" Then
n = CInt(Command(1))
ReDim a(1 To n) As Integer
ReDim u(1 To 2 * n - 1) As Integer
ReDim v(1 To 2 * n - 1) As Integer
For i = 1 To n
a(i) = i
Next
For i = 1 To 2 * n - 1
u(i) = 1
v(i) = 1
Next
m = 0
aux(n, 1, a(), u(), v(), m)
Print m
End If</lang>
=== Alternate version : iterative ===
<lang freebasic>Dim As Integer n, i, j, k, p, q
Dim m As LongInt = 0
If Command(1) <> "" Then
n = CInt(Command(1))
ReDim a(1 To n) As Integer
ReDim s(1 To n) As Integer
ReDim u(1 To 2 * n - 1) As Integer
ReDim v(1 To 2 * n - 1) As Integer
For i = 1 To n
a(i) = i
Next
For i = 1 To 2 * n - 1
u(i) = 1
v(i) = 1
Next
m = 0
i = 1
L1: If i > n Then
m += 1
For k = 1 To n : Print a(k); : Next : Print
Goto L4
End If
j = i
L2: k = a(j)
p = i - k + n
q = i + k - 1
If u(p) And v(q) Then
u(p) = 0 : v(q) = 0
a(j) = a(i) : a(i) = k
s(i) = j
i += 1
Goto L1
End If
L3: j += 1 : If j <= n Goto L2
L4: i -= 1 : If i = 0 Then Print m : End
j = s(i)
k = a(i) : a(i) = a(j) : a(j) = k
p = i - k + n
q = i + k - 1
u(p) = 1 : v(q) = 1
Goto L3
End If</lang>
=={{header|GAP}}==
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