46 lines
952 B
Text
46 lines
952 B
Text
# N-queens problem #
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INT ofs = 1, # Algol68 normally uses array offset of 1 #
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dim = 8; # dim X dim chess board #
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[ofs:dim+ofs-1]INT b;
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PROC unsafe = (INT y)BOOL:(
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INT x = b[y];
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BOOL safe := TRUE;
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FOR i TO y - LWB b WHILE safe DO
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INT t = b[y - i];
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IF t = x THEN safe := FALSE
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ELIF t = x - i THEN safe := FALSE
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ELIF t = x + i THEN safe := FALSE
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FI
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OD;
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NOT safe
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);
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INT s := 0;
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PROC print board = VOID:(
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print((new line, "Solution # ", s+:=1, new line));
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FOR y FROM LWB b TO UPB b DO
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FOR x FROM LWB b TO UPB b DO
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print("|"+(b[y]=x|"Q"|: ODD(x+y)|"/"|" "))
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OD;
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print(("|", new line))
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OD
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);
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# main # (
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INT y := LWB b;
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b[LWB b] := LWB b - 1;
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WHILE y >= LWB b DO
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WHILE IF (b[y]+:=1) <= UPB b THEN unsafe(y) ELSE FALSE FI DO SKIP OD;
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IF b[y] <= UPB b THEN
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IF y < UPB b THEN
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b[y+:=1] := LWB b - 1
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ELSE
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print board
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FI
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ELSE
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y-:=1
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FI
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OD
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)
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