Initial data commit

Task/N-queens-problem/IS-BASIC/n-queens-problem.basic

@@ -0,0 +1,38 @@
+100 PROGRAM "NQueens.bas"
+110 TEXT 80
+120 DO
+130   INPUT PROMPT "Size of board (2-12): ":N$
+140   LET N=VAL(N$)
+150 LOOP UNTIL N>1 AND N<13
+160 NUMERIC A(1 TO N),X(1 TO N),B(2 TO 2*N),C(-N+1 TO N-1)
+170 LET SOL=0
+180 CALL INIT(A):CALL INIT(B):CALL INIT(C)
+190 CALL TRY(1)
+200 PRINT SOL;"solutions."
+210 END
+220 DEF WRITE
+230   LET S$="":LET SOL=SOL+1
+240   FOR K=1 TO N
+250     LET S$=S$&CHR$(64+K)&STR$(X(K))&"  "
+260   NEXT
+270   PRINT S$
+280 END DEF
+290 DEF TRY(I)
+300   NUMERIC J
+310   FOR J=1 TO N
+320     IF A(J) AND B(I+J) AND C(I-J) THEN
+330       LET X(I)=J:LET A(J),B(I+J),C(I-J)=0
+340       IF I<N THEN
+350         CALL TRY(I+1)
+360       ELSE
+370         CALL WRITE
+380       END IF
+390       LET A(J),B(I+J),C(I-J)=1
+400     END IF
+410   NEXT
+420 END DEF
+430 DEF INIT(REF T)
+440   FOR I=LBOUND(T) TO UBOUND(T)
+450     LET T(I)=1
+460   NEXT
+470 END DEF