Question

代码：

puzzle1= [
          [7,0,0,0,0,0,2,1,8],
          [0,4,8,6,2,9,0,0,0],
          [0,0,3,0,0,1,0,0,0],
          [0,0,7,0,0,8,0,3,2],
          [0,0,9,7,0,6,5,0,0],
          [6,8,0,1,0,0,7,0,0],
          [0,0,0,2,0,0,4,0,0],
          [0,0,0,4,1,5,8,7,0],
          [3,5,4,0,0,0,0,0,6]
          ]  
def eliminate_values(puzzle):
    redo = False
    for i in range(9):
        for j in range(9):
            if puzzle[i][j]==0 or isinstance(puzzle[i][j], list):
                puzzle[i][j] = []
                for num in range(1,10):
                   num_check = True;
                   for x in range(9):
                       if puzzle[i][x]==num:
                           num_check = False
                       if puzzle[x][j]==num:
                           num_check = False
                       if i<3:
                           aa=0
                       elif i<6 and i>2:
                           aa=3
                       else:
                           aa=6
                       if j<3:
                           bb=0
                       elif j<6 and j>2:
                           bb=3
                       else:
                           bb=6
                       for a in range(3):
                           for b in range(3):
                               if puzzle[a+aa][b+bb]==num:
                                   num_check = False
                   if num_check:
                       puzzle[i][j].append(num)
                if len(puzzle[i][j]) == 1:
                    puzzle[i][j] = puzzle[i][j][0]
                    redo = True;
    if redo:
        eliminate_values(puzzle)
    else:
        print(puzzle)
        return puzzle

puzzle=eliminate_values(puzzle1)
print(puzzle)

控制台：

[[7, 9, 6, 3, 5, 4, 2, 1, 8], [1, 4, 8, 6, 2, 9, 3, 5, 7], [5, 2, 3, 8, 7, 1, 9, 6, 4], [4, 1, 7, 5, 9, 8, 6, 3, 2], [2, 3, 9, 7, 4, 6, 5, 8, 1], [6, 8, 5, 1, 3, 2, 7, 4, 9], [8, 7, 1, 2, 6, 3, 4, 9, 5], [9, 6, 2, 4, 1, 5, 8, 7, 3], [3, 5, 4, 9, 8, 7, 1, 2, 6]]
None

评论：

我是python的新手，但我不明白为什么print IS在函数内工作而不是在它返回主程序之后。（期望它打印两次，但只打印一次然后再打印

）

Answer 1

@tobias_k是对的。

在每个递归函数中，您都有一个基本案例和一个递归案例。基本情况是当你到达递归的末尾并从递归函数返回最终值时。递归情况是函数再次调用它自己。

你需要在两种情况下都返回。

如果你不这样做，那么即使你最终击中你的基本情况，基本情况的返回值也不会被传递到堆栈。

即：

def recursiveDecrement(x):
    if x > 0:
        print("Recursive case. x = %s" %x)
        recursiveDecrement(x - 1)
        print("I should have returned...x = %s" %x)
    else:
        print("Base case. x = %s" %x)
        return x

如果我拨打recursiveDecrement(5)，我的输出将是：

Recursive case. x = 5
Recursive case. x = 4
Recursive case. x = 3
Recursive case. x = 2
Recursive case. x = 1
Base case. x = 0
I should have returned...x = 1
I should have returned...x = 2
I should have returned...x = 3
I should have returned...x = 4
I should have returned...x = 5

但是，一旦命中基本情况，该方法就会继续执行，最后不会返回任何内容，x仍然等于5.

在两种情况下都要更改你的if语句，并且一切都应该有效。

if redo:
    return eliminate_values(puzzle)
else:
    return puzzle

Answer 2

如果$scope.ciudades = whatever you filtered; }为redo，则递归调用函数，并在堆栈的某处，True为redo后，打印并返回结果。但是，此结果不会在调用堆栈中向上传播，因此最外层函数调用将不返回任何内容，即False，然后打印。为此，您还必须None递归调用的结果：

return

或者，您可以将函数体包装在if redo: return eliminate_values(puzzle) # try again and return result else: return puzzle # result found in this try, return it循环中，而不是使用递归。

Python列表返回＆＃39;无＆＃39;

2 个答案: