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Problem

Level Order Sum

LeetCode #1161Medium
Sum each level with the level-batching loop

Given the root of a binary tree where the root is level 1 and each level below increments by one, return the smallest level number whose nodes have the largest sum of values.

Asked atAmazon
step 1 / 14
binary tree
9
3
15
20
7
queue (FIFO)
front →
(empty)
← back
BFS by level
▸
1levelSums(root):
2    queue = [root]
3    while queue not empty:
4        levelSize = len(queue)
5        sum = 0
6        for _ in range(levelSize):
7            node = queue.dequeue()
8            sum += node.val
9            enqueue node.children
10        levelSums.append(sum)
11    return levelSums   // max() for heaviest level
state
  • targetsum per level

line 1Goal: the SUM of the node values on each level — and from those, the heaviest level. This is the level-batching loop with a single accumulator added: dequeue a whole level, add each value into a running sum, then record that sum and reset.