二叉树层次遍历的两种写法

import collections


class BiTree(object):
    def __init__(self, val, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right


def nums_to_tree(nums):
    if not nums:
        return None
    queue = collections.deque()
    root = BiTree(nums[0])
    queue.append(root)
    i = 1
    while i < len(nums):
        node = queue.popleft()
        if i < len(nums) and nums[i] != -1:
            node.left = BiTree(nums[i])
            queue.append(node.left)
        i += 1

        if i < len(nums) and nums[i] != -1:
            node.right = BiTree(nums[i])
            queue.append(node.right)
        i += 1

    return root

# 层次遍历
# def level_sort(root):
#     if not root:
#         return None
#     queue = collections.deque()
#     queue.append(root)
#     while len(queue) > 0:  # 只要队不空，出队一个元素，并访问他的孩子节点
#         node = queue.popleft()
#         print(node.val, end="")
#         if node.left:
#             queue.append(node.left)
#         if node.right:
#             queue.append(node.right)


# 层次遍历
def level_sort(root):
    if not root:
        return None
    queue = collections.deque()
    queue.append(root)
    res = []
    while len(queue) > 0:  # 只要队不空，出队一个元素，并访问他的孩子节点
        for i in range(len(queue)):
            temp = []
            node = queue.popleft()
            temp.append(node.val)
            res.append(temp)
            if node.left:
                queue.append(node.left)
            if node.right:
                queue.append(node.right)
    print(res)


# 输入 1 null 1 null 1 2
#    1
#  /  \
# null  1
#      /  \
#   null  1
#        /
#       2
if __name__ == '__main__':
    nums = ['1', 'null', '1', 'null', '1', '2']
    nums = [int(i) if i != "null" else -1 for i in nums]
    root = nums_to_tree(nums)
    level_sort(root)