Construct a linked list from 2D matrix (Iterative Approach)

// C# to implement linked matrix 
// from a 2D matrix iteratively 
using System;
using System.Collections.Generic;

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

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

class GfG {

    // Function to construct the linked matrix 
    // from a List of Lists
    static Node Construct(List<List<int>> arr) {
        int m = arr.Count;  
        int n = arr[0].Count;  

        // Stores the head of the linked list
        Node mainhead = null;

        // List to store the heads of linked 
        // lists for each row
        List<Node> head = new List<Node>(m);

        Node rightcurr = null;

        // Create m linked lists by setting all the 
        // right nodes of every row
        for (int i = 0; i < m; i++) {
            head.Add(null);
            for (int j = 0; j < n; j++) {
                Node newptr = new Node(arr[i][j]);

                // Assign the first node as the mainhead
                if (mainhead == null) {
                    mainhead = newptr;
                }

                // Set the head for the row or link 
                // the current node
                if (head[i] == null) {
                    head[i] = newptr;
                } 
                else {
                    rightcurr.right = newptr;
                }

                rightcurr = newptr;
            }
        }

        // Set the down pointers for nodes 
        // in consecutive rows
        for (int i = 0; i < m - 1; i++) {
            Node curr1 = head[i];
            Node curr2 = head[i + 1];

            // Link corresponding nodes in 
            // consecutive rows
            while (curr1 != null && curr2 != null) {
                curr1.down = curr2;
                curr1 = curr1.right;
                curr2 = curr2.right;
            }
        }

        // Return the mainhead of the 
        // constructed linked list
        return mainhead;
    }

    static void PrintList(Node head) {
        Node currRow = head;
        while (currRow != null) {
            Node currCol = currRow;
            while (currCol != null) {
                Console.Write(currCol.data + " ");
                currCol = currCol.right;
            }
            Console.WriteLine();
            currRow = currRow.down;
        }
    }

    static void Main(string[] args) {
      
        List<List<int>> arr = new List<List<int>> {
            new List<int> { 1, 2, 3 },
            new List<int> { 4, 5, 6 },
            new List<int> { 7, 8, 9 }
        };

        Node head = Construct(arr);
        PrintList(head);
    }
}