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[pdp8.git] / sw / src / pascal / KNIGHT.PS

PROGRAM KNIGHTSTOUR(OUTPUT);

CONST N = 5; NSQ = 25;

VAR   I,J: INTEGER;
      Q: BOOLEAN;
      A,B: ARRAY[1..8] OF INTEGER;
      H: ARRAY[1..N,1..N] OF INTEGER;

PROCEDURE TRY(I: INTEGER; X,Y: INTEGER; VAR Q: BOOLEAN);
   VAR K,U,V: INTEGER; Q1: BOOLEAN;
BEGIN K := 0;
   REPEAT K:= K+1; Q1 := FALSE;
      U := X + A[K]; V := Y + B[K];
      IF (1<=U) AND (U<=N) AND (1<=V) AND (V<=N) THEN
        IF H[U,V] = 0 THEN
        BEGIN H[U,V] := I;
           IF I < NSQ THEN
              BEGIN TRY(I+1,U,V,Q1);
                IF NOT Q1 THEN H[U,V] := 0
              END ELSE Q1 := TRUE
        END
   UNTIL Q1 OR (K=8);
   Q := Q1
END (* TRY *);

BEGIN
   A[1] :=  2; B[1] :=  1;
   A[2] :=  1; B[2] :=  2;
   A[3] := -1; B[3] :=  2;
   A[4] := -2; B[4] :=  1;
   A[5] := -2; B[5] := -1;
   A[6] := -1; B[6] := -2;
   A[7] :=  1; B[7] := -2;
   A[8] :=  1; B[8] := -1;

   FOR I := 1 TO N DO
      FOR J := 1 TO N DO H[I,J] := 0;
   H[1,1] := 1; TRY(2,1,1,Q);
   IF Q THEN
      FOR I := 1 TO N DO
      BEGIN FOR J := 1 TO N DO WRITE( H[I,J] :5);
         WRITELN
      END
   ELSE WRITELN("KEINE LOESUNG!")
END.