Turbo Prolog

string word ("" , [ 1 ) : -! .
string:word(Str,[HIT1):bound(Str),frontstr(1,Str,H,S),string_word(S,T).string_word(Str,[HIT1):free(Str),bound(H),string_word(S,T),concat(H,T,Str).
append( [1 ,L,L) :-!.
append([XIL11,L2,[XIL31)
repeat.
repeat:-repeat.
THE N QUEENS PROBLEM
append(L1,L2,L3).
In the N Queens problem, we try to place N queens on a chessboard in such a way that
no two queens can take each other. Thus, no two queens can be placed on the same
row, column or diagonal.
To solve the problem, we'll number the rows and columns of the chessboard from I
to N. To number the diagonals, we divide them into two types, so that a diagonal
is uniquely specified by a type and a number calculated from its row and column
numbers:
Diagonal = N + Column - Row
Diagonal = Row + Column - 1
(type 1)
(type 2)
When the chessboard is viewed with row I at the top and column I on the left side,
type I diagonals resemble the "\" character in shape and type 2 diagonals resemble the
shape of"/". The numbering of type 2 diagonals on a 414 board is shown in Figure 10-4.
I 2 3 4
I I 2 3 4
2 2 3 4 5
3 3 4 5 6
4 4 5 6 7
Figure 10-4 The N Queens Chessboard
To solve the N Queens problem with a Turbo Prolog program, we must record which
rows, columns and diagonals are free and also make a note of where the queens are
placed.
A queen's position is described with a row number and a column number, as in the
domain declaration
Tutorial VIII: Spreading Your Wings 121