Make a little progress every day , It's already great , Insist on , Don't be too tired , Refuse to roll in , Start with practice every day , Ten minutes a day , Live happily all your life ！ The epidemic is still repeated , Everyone wear masks ~ Continue to continue , Come on , Today and Brother cheshen Work together to improve your Python Programming and Interview ability Well , brush ladder on high buildings ~

Put on what I took Photo Well ！

Recommend a song every day ： Maple ——Jay Chou

The following is my Ladder integral rule ：

At least one question a day ： An integral +10 branch
If you do one more question （ Or one more way to answer ）, Then the points of the day +20 branch （+10+10）
If you do more than three , Start with question 3 +20 branch （ Such as ： If you do three questions, you will score -10+10+20=40; If you do four questions, you will score –10+10+20+20=60）

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Initial classification 100 branch
If you haven't done the problem for one day , Then deduct points -10 branch （ Saturday 、 Except Sunday ： rest ）
insist ！！！

Primary algorithm

List of questions

Linked list

stem

Give you a binary tree , Please return to its button Sequence traversal The resulting node value . （ That is, layer by layer , Access all nodes from left to right ）.

Example ：
Binary tree ：[3,9,20,null,null,15,7],

Return its sequence traversal result ：

Breadth first search

analysis ：

Returns an array of , We also need to initialize the array , But I don't know the size of the array , So it's usually stored in list And then convert it into an array , return list It's simpler .

Borrow the big guy's picture again , That's perfect ！

class Solution: def levelOrder(self, root: TreeNode) -> List[List[int]]: if not root: return [] queue = [root] res = [] while queue: n = len(queue) sub_list = [] for i in range(n): node = queue.pop(0) sub_list.append(node.val) if node.left: queue.append(node.left) if node.right: queue.append(node.right) res.append(sub_list) return res

The result is right , Today is also a tiring day , Come here first , Resting ！~

Share today , Yongge （ Maybe it's kind to call it this way ） Finally, let's say our best wishes ！~

Reference

author ： Power button (LeetCode)
link ：https://leetcode-cn.com/leetbook/read/top-interview-questions-easy/xnarn7/
source ： Power button （LeetCode）

author ： Data structures and algorithms
link ：https://leetcode-cn.com/leetbook/read/top-interview-questions-easy/xnd69e/?discussion=1Pu6Hw
source ： Power button （LeetCode）

Score today ：+10
Total score ：710

come on. ！！！