Find the maximum path sum between two leaves of a binary tree

// C# program to find maximum path 
// sum between two leaves of a binary tree
using System;

class Node {
    public int data;
    public Node left, right;

    public Node(int x) {
        data = x;
        left = right = null;
    }
}

class GfG {
  
    // mxPathSum function to calculate maximum path sum between two leaves
    // and maximum sum from node to leaf in a single traversal
    static int mxPathSum(Node root, ref int maxPathSum) {
      
        // Base case: If the node is null, return 0
        if (root == null) {
            return 0;
        }

        // Recursively calculate the maximum sum from 
        // node to leaf for left and right subtrees
        int mxLeft = mxPathSum(root.left, ref maxPathSum);
        int mxRight = mxPathSum(root.right, ref maxPathSum);

        // If both left and right children exist, 
      	// update maxPathSum
        if (root.left != null && root.right != null) {
          
            // This is the sum of the left path, 
            // right path, and the node's data
            int maxSumPathViaNode = mxLeft + mxRight + root.data;

            // Update the maximum sum path between 
          	// two leaves
            maxPathSum = Math.Max(maxPathSum, maxSumPathViaNode);

            // Return the maximum sum from the current 
          	// node to a leaf
            return root.data + Math.Max(mxLeft, mxRight);
        }

        // If only one child exists, return the sum from
      	// the node to leaf
        return root.data + 
          (root.left != null ? mxLeft : mxRight);
    }

    // Function to return the maximum path 
    // sum between any two leaves in the binary tree
    static int FindMaxSum(Node root) {
      
        // Edge case: If the tree is empty,
      	// return 0
        if (root == null) {
            return 0;
        }

        int maxPathSum = int.MinValue;

        // Call the helper function to 
      	// compute the result
        mxPathSum(root, ref maxPathSum);

        return maxPathSum;
    }

    static void Main(string[] args) {
      
        // Construct a sample binary tree
        //
        //         1
        //       /   \
        //     -2     3
        //     / \   / \
        //    8  -1  4  -5
    
        Node root = new Node(1);
        root.left = new Node(-2);
        root.right = new Node(3);
        root.left.left = new Node(8);
        root.left.right = new Node(-1);
        root.right.left = new Node(4);
        root.right.right = new Node(-5);

        int result = FindMaxSum(root);
        Console.WriteLine(result);
    }
}