递归函数返回祖先和后继者之间的界线

Question

我需要编写一个递归函数，如果存在，则返回祖先和后继者之间的界线。该函数将祖先、继任者和孩子及其父母的字典作为参数。我目前拥有的代码在某些情况下有效，但并非全部有效，所以它肯定还缺少一些东西。我目前尝试使用列表来添加人名，但我需要以某种方式将它们一一打印出来，结果最终。这就是我所拥有的和示例。前 4 个有效，但最后 3 个无效。在看第一个例子的时候，基本上它需要返回的是

Lucia
Adele
Sam
John

table = {'John': ('Sam', 'Mary'),
            'Mary': ('Konstantin', 'Marie'),
            'Rita': ('Sam', 'Mary'),
            'Simon': ('Sam', 'Mary'),
            'Marie': ('Carl', 'Liz'),
            'Sam': ('Joseph', 'Adele'),
            'Adele': ('Johannes', 'Lucia'),
            'Konstantin': ('Viktor', 'Jelena'),
            'Joseph': ('August', 'Emma'),
            'Viktor': ('Nikolai', 'Maria')}

def return_line(ancestor, successor, table, line = []):
    if successor in table:
        parents = table[successor]
        if ancestor in parents:
            if ancestor not in line:
                line.append(ancestor)
            if successor not in line:
                line.append(successor)         
        else:
            successor_1 = parents[0]
            successor_2 = parents[1]
            return_line(ancestor, successor_1, table)
            if line == []:
                return_line(ancestor, successor_2, table)
            else:
                ancestor = line[-1]
                return_line(ancestor, successor, table)            
    else:
        return
    if line != []:
        return line
    else:
        return("Doesn't exist")

print(return_line("Lucia", "John", table))
print(return_line("Marie", "Adele", table))
print(return_line("Maria", "Mary", table))
print(return_line("Emma", "Rita", table))

print(return_line("Nikolai", "John", table))
print(return_line("Jelena", "John", table))
print(return_line("Carl", "Mary", table))

Answer 1

一个更简单的实现，无需传递可变参数：

def line(ancestor, successor, table):
    if ancestor == successor:
        return [successor]
    if successor not in table:
        return  # no line exists
    for parent in table[successor]:
        anc_line = line(ancestor, parent, table)
        if anc_line:
            return anc_line + [successor] 

line("Lucia", "John", table)
# ['Lucia', 'Adele', 'Sam', 'John']
line("Marie", "Adele", table)
# None
line("Maria", "Mary", table)
# ['Maria', 'Viktor', 'Konstantin', 'Mary']
line("Emma", "Rita", table)
# ['Emma', 'Joseph', 'Sam', 'Rita']
line("Nikolai", "John", table)
# ['Nikolai', 'Viktor', 'Konstantin', 'Mary', 'John']
line("Jelena", "John", table)
# ['Jelena', 'Konstantin', 'Mary', 'John']
line("Carl", "Mary", table)
# ['Carl', 'Marie', 'Mary']

基本情况：
1.ancestor == successor:一人构成单例线
2.successor not in table：没有这个人父母的更多信息，所以没有必要再去寻找了

递归：
1. 找到从祖先到任一父的线
2.如果存在，追加手头的人