Skip to main content

Binary Tree Maximum Path Sum

Problem statement​

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.

Example 1:

Input: root = [1,2,3]Output: 6Explanation: The optimal path is 2 -> 1 -> 3 with a path sum of 2 + 1 + 3 = 6.

Example 2:

Input: root = [-10,9,20,null,null,15,7]Output: 42Explanation: The optimal path is 15 -> 20 -> 7 with a path sum of 15 + 20 + 7 = 42.

Constraints:

  • The number of nodes in the tree is in the range [1, 3 * 104].
  • -1000 <= Node.val <= 1000

My 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 maxValue = Number.MIN_SAFE_INTEGER;
    function traverse(node) {
        if (!node) {
            return 0;
        }
        
        const left = Math.max(0, traverse(node.left));
        const right = Math.max(0, traverse(node.right))
        maxValue = Math.max(maxValue, left + right + node.val);
        // console.log(left, right, node.val, maxValue);
        return Math.max(left, right) + node.val;
    }
        
    traverse(root);
    // console.log(maxValue);
    return maxValue;
    
    
};