python —— 树的遍历 —— 深度优先遍历（先序、中序、后序）

代码：

# 2**n - 1  # 全二叉树
# n=4 2**4 - 1 = 15
import random
node_v = [2,3,5,7,11,0,17,19,23,0,0,0,0,41,43]
# node_v = list(range(0, 15))
# random.shuffle(node_v)
# print(node_v) # [14, 4, 12, 0, 1, 13, 9, 11, 3, 5, 6, 10, 2, 7, 8]
              # [0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14]
class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right 
node_list = [TreeNode(i) for i in node_v] # 初始化生成所有节点
node_list[5], node_list[9], node_list[10], node_list[11], node_list[12] = None, None, None, None, None
print(node_list)

for i in range(len(node_list)):           # 将父节点与左右节点进行连接
    node = node_list[i]  # TreeNode对象
    if 2*i+1 < len(node_list):
        if node != None:
            node.left = node_list[2*i+1]  # node.left == None
    if 2*i+2 < len(node_list):
        if node != None:
            node.right = node_list[2*i+2]

root_node = node_list[0]

def preorder_traversal(root):
    if root is None:
        return None 
    # return [root.val] + preorder_traversal(root.left) + preorder_traversal(root.right)
    print(root.val)
    preorder_traversal(root.left)
    preorder_traversal(root.right)

def midorder_traversal(root):
    if root is None:
        return None 
    # return [root.val] + preorder_traversal(root.left) + preorder_traversal(root.right)
    midorder_traversal(root.left)
    print(root.val)
    midorder_traversal(root.right)

def postorder_traversal(root):
    if root is None:
        return None 
    # return [root.val] + preorder_traversal(root.left) + preorder_traversal(root.right)
    postorder_traversal(root.left)
    postorder_traversal(root.right)
    print(root.val)

# preorder_traversal(root_node)
# midorder_traversal(root_node)
postorder_traversal(root_node)

运行效果：（后序遍历）