后续遍历-python

# 后续遍历是，左右根，逆序是 根右左，
# 和前序遍历很像，利用前序遍历的方法实现根右左的遍历
# 然后逆序打印

def pos_order(root):
    if not root:
        print("")
    
    stack = []  # 用来实现根右左的遍历
    temp = [] # 中间结果
    stack.append(root)
    while len(stack):
        pop = stack.pop()
        temp.append(pop.val)
        if pop.left != None:
            stack.append(pop.left)
        if pop.right != None:
            stack.append(pop.right)
    n = len(temp) 
    for i in range(n):
        print(temp[n-1-i],sep=" ")