1161. Maximum Level Sum of a Binary Tree

Problem Link

Description

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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

Solution

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Python3

# 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:
        res, level = root.val, 1
        queue = deque([root])
        currLevel = 1
 
        while queue:
            N = len(queue)
            curr = 0
 
            for _ in range(N):
                node = queue.popleft()
                curr += node.val
 
                for leaf in (node.left, node.right):
                    if leaf:
                        queue.append(leaf)
 
            if curr > res:
                res = curr
                level = currLevel
            
            currLevel += 1
 
        return level