binary-tree-maximum-path-sum.js

/**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. */

/**
 * 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 max = -Infinity;
    
    function dfs(node) {
      if (node === null) {
        return 0;
      }
      let leftH = Math.max(0, dfs(node.left));
      let rightH = Math.max(0, dfs(node.right));
      max = Math.max(max, leftH + rightH + node.val);
      return node.val + Math.max(leftH, rightH);
      
    }
    
    dfs(root);
    return max;
      
  };