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).

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