# LeetCode 1161. Maximum Level Sum of a Binary Tree

## Description

https://leetcode.com/problems/maximum-level-sum-of-a-binary-tree/

Given the `root` of a binary tree, the level of its root is `1`, the level of its children is `2`, and so on.

Return the smallest level `x` such that the sum of all the values of nodes at level `x` is maximal.

Example 1:

```Input: root = [1,7,0,7,-8,null,null]
Output: 2
Explanation:
Level 1 sum = 1.
Level 2 sum = 7 + 0 = 7.
Level 3 sum = 7 + -8 = -1.
So we return the level with the maximum sum which is level 2.
```

Example 2:

```Input: root = [989,null,10250,98693,-89388,null,null,null,-32127]
Output: 2
```

Constraints:

• The number of nodes in the tree is in the range `[1, 104]`.
• `-105 <= Node.val <= 105`

## Explanation

Conduct level order traverse and find out the level with the maximum sum.

## Python Solution

``````# 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
class Solution:
def maxLevelSum(self, root: Optional[TreeNode]) -> int:
if not root:
return 0

max_level_sum = -sys.maxsize

queue = []
queue.append(root)

levels = []

while queue:
size = len(queue)

level = []
for i in range(size):
node = queue.pop(0)
level.append(node.val)

if node.left:
queue.append(node.left)

if node.right:
queue.append(node.right)

levels.append(sum(level))

return levels.index(max(levels)) + 1``````
• Time Complexity: O(N).
• Space Complexity: O(N).