八皇后問題:
在8×8格的國際象棋上擺放八個皇后,使其不能互相攻擊,即任意兩個皇后都不能處於同一行、同一列或同一斜線上,問有多少種擺法
def conflict(chesses_placed, next_chess_xcor):
"""
This is a conflicting function defined
:param chesses_placed: use a tuple to save chesses placed
:param next_chess_xcor: the x coordinate of next chess to place
:return: true or false
"""
# get the next y coordinate by chessed placed
next_chess_ycor = len(chesses_placed)
# use next chess y coordinate to confirm the count of loop
for i in range(next_chess_ycor):
# use absolute value to confirm the same oblique line
if abs(chesses_placed[i] - next_chess_xcor) in (0, abs(i - next_chess_ycor)):
return True
return False
def place_queens(num=8, chesses_placed_tuple=()):
"""
This is a placing queens function defined
:param num: the count of queens
:param chesses_placed_tuple: such as (1, 5, 0)
:return: a generator
"""
for i in range(num):
if not conflict(chesses_placed_tuple, i):
# judge the last line
if len(chesses_placed_tuple) == num - 1:
yield (i,)
else:
# get one bye one element from the generator
for j in place_queens(num, chesses_placed_tuple + (i,)):
# superimpose elements to the newest tuple
yield (i,) + j
res = list(place_queens(8))
print(res)
print(len(res))
簡版:
def queen(A, cur=0):
if cur == len(A):
print(A)
return 0
for col in range(len(A)):
A[cur], flag = col, True
for row in range(cur):
if A[row] == col or abs(col - A[row]) == cur - row:
flag = False
break
if flag:
queen(A, cur+1)
queen([None]*8)