二叉树的遍历

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# -*- coding: utf-8 -*-

from collections import deque


class BiTreeNode:
    def __init__(self, data):
        self.data = data
        self.lchild = None  # 左孩子
        self.rchild = None  # 右孩子


a = BiTreeNode("A")
b = BiTreeNode("B")
c = BiTreeNode("C")
d = BiTreeNode("D")
e = BiTreeNode("E")
f = BiTreeNode("F")
g = BiTreeNode("G")

e.lchild = a
e.rchild = g
a.rchild = c
c.lchild = b
c.rchild = d
g.rchild = f

root = e


# 前序遍历
def pre_order(root):
    if root:
        print(root.data, end=',')
        pre_order(root.lchild)
        pre_order(root.rchild)


# 中序遍历
def in_order(root):
    if root:
        in_order(root.lchild)
        print(root.data, end=',')
        in_order(root.rchild)


# 后序遍历
def post_order(root):
    if root:
        post_order(root.lchild)
        post_order(root.rchild)
        print(root.data, end=',')


# 层次遍历
def level_order(root):
    queue = deque()
    queue.append(root)
    while len(queue) > 0:  # 只要队不空
        node = queue.popleft()
        print(node.data, end=',')
        if node.lchild:
            queue.append(node.lchild)
        if node.rchild:
            queue.append(node.rchild)


level_order(root)