#1161 - Maximum Level Sum of a Binary Tree

MediumBinary Tree - BFS

Given the root of a binary tree, return the smallest level number (1-indexed) that has the maximum sum of node values.

Input	Output
root = [1,7,0,7,-8,null,null]	2
root = [989,null,10250,98693,-89388,null,null,null,-32127]	2

Solution Space

Try it

/**
 * Returns the 1-indexed level with the maximum sum of values.
 *
 * @param root Root of the binary tree
 * @returns Level number (1-indexed) with the greatest sum
 */
export function maxLevelSum(root: TreeNode | null): number {
  if (!root) return 0;

  const queue: TreeNode[] = [root];
  let maxSum = -Infinity;
  let maxLevel = 1;
  let level = 0;

  while (queue.length > 0) {
    level++;
    const size = queue.length;
    let levelSum = 0;

    for (let i = 0; i < size; i++) {
      const node = queue.shift()!;
      levelSum += node.val;
      if (node.left) queue.push(node.left);
      if (node.right) queue.push(node.right);
    }

    if (levelSum > maxSum) {
      maxSum = levelSum;
      maxLevel = level;
    }
  }

  return maxLevel;
}

Approach: BFS level-order – sum each level's values, track the level with the highest sum.

Time: O(n) – every node processed once.

Space: O(n) – queue width.

#199 Binary Tree Right Side View

#450 Delete Node in a BST