#124 - Binary Tree Maximum Path Sum

Hard • View on LeetCode • View on GitHub

Problem Description

A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them. A node can only appear in the sequence at most once. Note that the path does not need to pass through the root.

The path sum of a path is the sum of the node's values in the path.

Given the root of a binary tree, return the maximum path sum of any non-empty path.

Solution

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */
var maxPathSum = function(root) {
  let result = -Infinity;

  function traverse(node) {
    if (!node) return 0;
    const leftValue = Math.max(traverse(node.left), 0);
    const rightValue = Math.max(traverse(node.right), 0);
    result = Math.max(result, node.val + leftValue + rightValue);
    return node.val + Math.max(leftValue, rightValue);
  }

  traverse(root);

  return result;
};