Data commit

Task/N-queens-problem/SNOBOL4/n-queens-problem.sno

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+* N queens problem
+* Set N to the desired number.  The program prints out all solution boards.
+	N = 5
+	NM1 = N - 1; NP1 = N + 1; NSZ = N * NP1; &STLIMIT = 10 ** 9; &ANCHOR = 1
+	DEFINE('SOLVE(B)I')
+* This pattern tests if the first queen attacks any of the others:
+	TEST = BREAK('Q') 'Q' (ARBNO(LEN(N) '-') LEN(N) 'Q'
++	      | ARBNO(LEN(NP1) '-') LEN(NP1) 'Q'
++	      | ARBNO(LEN(NM1) '-') LEN(NM1) 'Q')
+	P = LEN(NM1) . X LEN(1); L = 'Q' DUPL('-',NM1) ' '
+	SOLVE()        :(END)
+SOLVE	EQ(SIZE(B),NSZ) 	    :S(PRINT)
+* Add another row with a queen:
+	B = L B
+LOOP	I = LT(I,N) I + 1 :F(RETURN)
+	B TEST :S(NEXT)
+	SOLVE(B)
+* Try queen in next square:
+NEXT	B P = '-' X :(LOOP)
+PRINT	SOLUTION = SOLUTION + 1
+	OUTPUT = 'Solution number ' SOLUTION ' is:'
+PRTLOOP B LEN(NP1) . OUTPUT = :S(PRTLOOP)F(RETURN)
+END