Leetcode daily question - 515 Find the maximum value in each tree row

subject

Given the root node of a binary tree root , Please find the maximum value of each layer in the binary tree .

Example

Example 1：

Input : root = [1,3,2,5,3,null,9]
Output : [1,3,9]

Example 2：

Input : root = [1,2,3]
Output : [1,3]

Tips ：

The range of the number of nodes in a binary tree is [0,104]
-231 <= Node.val <= 231 - 1

Ideas

BFS, Simulating sequence traversal using queues , List the maximum value of each layer

Answer key

# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, val=0, left=None, right=None):
# self.val = val
# self.left = left
# self.right = right
from collections import deque
class Solution:
    def largestValues(self, root: Optional[TreeNode]) -> List[int]:
    	#  Queue and result list 
        temp,res = deque(), []
        if root is None:
            return res
        else:
            temp.append(root)
        while temp:
            n, max_ = len(temp), -float('inf')
            #  Update the maximum value of each layer 
            for i in range(n):
                index = temp.popleft()
                max_ = max(max_, index.val)
                if index.left is not None:
                    temp.append(index.left)
                if index.right is not None:
                    temp.append(index.right)
            res.append(max_)
        return res