二叉树

Posted 2023-01-24 月色真美丶

　　二叉树是由n个节点构成，它有可能是空树，也有可能是非空树。

　　对于非空树，有且仅有一个根节点，和左右两个不相交的左子树和右子树

　　左子树和右子树有左右之分，不可颠倒

　　二叉树的遍历法;

　　1.深度优先法

　　　　前序遍历，访问根节点，遍历左子树，再遍历右子树

　　　　中序遍历，遍历左子树，访问根节点，再遍历右子树

　　　　后序遍历，遍历左子树，遍历右子树，再访问根节点

　　2.广度优先法

　　　　层级遍历，从根节点开始一层一层的自左向右遍历节点　　　　

 

　　代码实现：

　　

# -*- coding = utf-8 -*-
# @Author: Wchime
# @time: 2023/1/23 14:09
# @file: 二叉树.py


class Node(object):
    """
    树节点，包含值和左右子节点
    """
    def __init__(self, item):
        self.item = item
        self.lchild = None
        self.rchild = None


class Tree(object):
    """
    二叉树
    """
    def __init__(self):
        self.__root = None

    def is_empty(self):
        """
        判断树是否为空
        :return:
        """
        return self.__root is None

    def append(self, item):
        """
        添加节点
        :param item:
        :return:
        """
        node = Node(item)

        if self.is_empty():
            self.__root = node
            return
        else:
            li = [self.__root]
            while li:
                cur = li.pop(0)
                if cur.lchild is None:
                    cur.lchild = node
                    return
                else:
                    li.append(cur.lchild)
                if cur.rchild is None:
                    cur.rchild = node
                    return
                else:
                    li.append(cur.rchild)

    def travel_preorder(self):
        """
        先序遍历
        :return:
        """
        def recur(node):
            """
            递归
            :return:
            """
            if node is None:
                # print(\'None\')
                return
            print(node.item, end="  ")
            recur(node.lchild)
            recur(node.rchild)

        recur(self.__root)
        print(\'\\n\')

    def travel_inorder(self):
        """
        中序遍历
        :return:
        """
        def recur(node):
            """
            递归
            :return:
            """
            if node is None:
                # print(\'None\')
                return
            recur(node.lchild)
            print(node.item, end="  ")
            recur(node.rchild)

        recur(self.__root)
        print(\'\\n\')

    def travel_postorder(self):
        def recur(node):
            """
            递归
            :return:
            """
            if node is None:
                # print(\'None\')
                return
            recur(node.lchild)
            recur(node.rchild)
            print(node.item, end="  ")

        recur(self.__root)
        print(\'\\n\')

    def travel_breadth(self):
        """
        广度优先遍历
        :return:
        """
        if self.__root is None:
                return

        li = [self.__root]
        while li:
            cur = li.pop(0)
            print(cur.item, end="  ")
            if cur.lchild is not None:
                li.append(cur.lchild)
            if cur.rchild is not None:
                li.append(cur.rchild)
        print(\'\\n\')


if __name__ == "__main__":
    tree = Tree()
    print(tree.is_empty())
    tree.append(3)
    tree.append(7)
    tree.append(9)
    tree.append(5)
    tree.append(2)
    tree.append(1)
    tree.travel_preorder()
    tree.travel_inorder()
    tree.travel_postorder()

    tree.travel_breadth()