LeetCode-in-All

124. Binary Tree Maximum Path Sum

Hard

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: 6

Explanation: 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: 42

Explanation: The optimal path is 15 -> 20 -> 7 with a path sum of 15 + 20 + 7 = 42.

Constraints:

Solution

using LeetCodeNet.Com_github_leetcode;

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int val=0, TreeNode left=null, TreeNode right=null) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
public class Solution {
    private int max = int.MinValue;

    private int Helper(TreeNode root) {
        if (root == null) {
            return 0;
        }
        // to avoid the -ve values in left side we will compare them with 0
        int left = Math.Max(0, Helper(root.left));
        int right = Math.Max(0, Helper(root.right));
        int current = (int)(root.val + left + right);
        if (current > max) {
            max = current;
        }
        return (int)(root.val + Math.Max(left, right));
    }

    public int MaxPathSum(TreeNode root) {
        Helper(root);
        return max;
    }
}