Python程序：使用BFS遍历显示树的节点

当需要使用广度优先搜索遍历来显示树的节点时，需要创建一个类，其中包含设置根节点、向树中添加元素、搜索指定元素、执行”BFS”（广度优先搜索）等方法。可以创建该类的实例来访问和使用这些方法。

下面是一个示例：

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例子

class Tree_struct:
    def __init__(self, data=None):
        self.key = data
        self.children = []

    def set_root(self, data):
        self.key = data

    def add_node(self, node):
        self.children.append(node)

    def search_node(self, key):
        if self.key == key:
            return self
        for child in self.children:
            temp = child.search_node(key)
            if temp is not None:
                return temp
        return None

    def bfs_operation(self):
        queue = [self]
        while queue != []:
            popped = queue.pop(0)
            for child in popped.children:
                queue.append(child)
            print(popped.key, end=' ')

my_instance = None

print('Menu (assume no duplicate keys)')
print('add <data> at root')
print('add <data> below <data>')
print('bfs')
print('quit')

while True:
    my_input = input('What operation would you do ? ').split()

    operation = my_input[0].strip().lower()
    if operation == 'add':
        data = int(my_input[1])
        new_node = Tree_struct(data)
        suboperation = my_input[2].strip().lower()
        if suboperation == 'at':
            my_instance = new_node
        elif suboperation == 'below':
            position = my_input[3].strip().lower()
            key = int(position)
            ref_node = None
            if my_instance is not None:
                ref_node = my_instance.search_node(key)
            if ref_node is None:
                print('No such key')
                continue
            ref_node.add_node(new_node)

    elif operation == 'bfs':
        if my_instance is None:
            print('The tree is empty')
        else:
            print('Breadth First Search traversal is : ', end='')
            my_instance.bfs_operation()
            print()

    elif operation == 'quit':
        break

输出

Menu (assume no duplicate keys)
add <data> at root
add <data> below <data>
bfs
quit
What operation would you do ? add 6 at root
What operation would you do ? add 4 below 6
What operation would you do ? add 9 below 4
What operation would you do ? bfs
Breadth First Search traversal is : 6 4 9
What operation would you do ? quit