tasks a-s

Task/N-queens-problem/Python/n-queens-problem-1.py

@@ -0,0 +1,8 @@
+from itertools import permutations
+
+n = 8
+cols = range(n)
+for vec in permutations(cols):
+    if n == len(set(vec[i]+i for i in cols)) \
+         == len(set(vec[i]-i for i in cols)):
+        print ( vec )

Task/N-queens-problem/Python/n-queens-problem-2.py

@@ -0,0 +1,2 @@
+def board(vec):
+    print ("\n".join('.' * i + 'Q' + '.' * (n-i-1) for i in vec) + "\n===\n")

Task/N-queens-problem/Python/n-queens-problem-3.py

@@ -0,0 +1,17 @@
+# From: http://wiki.python.org/moin/SimplePrograms, with permission from the author, Steve Howell
+BOARD_SIZE = 8
+
+def under_attack(col, queens):
+    return col in queens or \
+           any(abs(col - x) == len(queens)-i for i,x in enumerate(queens))
+
+def solve(n):
+    solutions = [[]]
+    for row in range(n):
+        solutions = [solution+[i+1]
+                       for solution in solutions
+                       for i in range(BOARD_SIZE)
+                       if not under_attack(i+1, solution)]
+    return solutions
+
+for answer in solve(BOARD_SIZE): print(list(enumerate(answer, start=1)))

Task/N-queens-problem/Python/n-queens-problem-4.py

@@ -0,0 +1,19 @@
+BOARD_SIZE = 8
+
+def under_attack(col, queens):
+    return col in queens or \
+           any(abs(col - x) == len(queens)-i for i,x in enumerate(queens))
+
+def solve(n):
+    solutions = [[]]
+    for row in range(n):
+        solutions = (solution+[i+1]
+                       for solution in solutions # first for clause is evaluated immediately,
+                                                 # so "solutions" is correctly captured
+                       for i in range(BOARD_SIZE)
+                       if not under_attack(i+1, solution))
+    return solutions
+
+answers = solve(BOARD_SIZE)
+first_answer = next(answers)
+print(list(enumerate(first_answer, start=1)))