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Construct a linked list from 2D matrix
• Difficulty Level : Medium
• Last Updated : 26 Nov, 2019

Given a matrix. Convert it into a linked list matrix such that each node is connected to its next right and down node.

Example:

```Input : 2D matrix
1 2 3
4 5 6
7 8 9

Output :
1 -> 2 -> 3 -> NULL
|    |    |
v    v    v
4 -> 5 -> 6 -> NULL
|    |    |
v    v    v
7 -> 8 -> 9 -> NULL
|    |    |
v    v    v
NULL NULL NULL
```

Question Source : Factset Interview Experience | Set 9

## Recommended: Please solve it on PRACTICE first, before moving on to the solution.

The idea is to construct a new node for every element of matrix and recursively create its down and right nodes.

## C++

 `// CPP program to construct a linked list``// from given 2D matrix``#include ``using` `namespace` `std;`` ` `// struct node of linked list``struct` `Node {``    ``int` `data;``    ``Node* right, *down;``};`` ` `// returns head pointer of linked list``// constructed from 2D matrix``Node* construct(``int` `arr[][3], ``int` `i, ``int` `j, ``                              ``int` `m, ``int` `n)``{``    ``// return if i or j is out of bounds``    ``if` `(i > n - 1 || j > m - 1)``        ``return` `NULL;`` ` `    ``// create a new node for current i and j``    ``// and recursively allocate its down and``    ``// right pointers``    ``Node* temp = ``new` `Node();``    ``temp->data = arr[i][j];``    ``temp->right = construct(arr, i, j + 1, m, n);``    ``temp->down  = construct(arr, i + 1, j, m, n);``    ``return` `temp;``}`` ` `// utility function for displaying``// linked list data``void` `display(Node* head)``{``    ``// pointer to move right``    ``Node* Rp;`` ` `    ``// pointer to move down``    ``Node* Dp = head;`` ` `    ``// loop till node->down is not NULL``    ``while` `(Dp) {``        ``Rp = Dp;`` ` `        ``// loop till node->right is not NULL``        ``while` `(Rp) {``            ``cout << Rp->data << ``" "``;``            ``Rp = Rp->right;``        ``}``        ``cout << ``"\n"``;``        ``Dp = Dp->down;``    ``}``}`` ` `// driver program``int` `main()``{``    ``// 2D matrix``    ``int` `arr[][3] = {``        ``{ 1, 2, 3 },``        ``{ 4, 5, 6 },``        ``{ 7, 8, 9 }``    ``};`` ` `    ``int` `m = 3, n = 3;``    ``Node* head = construct(arr, 0, 0, m, n);``    ``display(head);``    ``return` `0;``}`

## Java

 `// Java program to construct a linked list``// from given 2D matrix``public` `class` `Linked_list_2D_Matrix {`` ` `    ``// node of linked list``    ``static` `class` `Node {``        ``int` `data;``        ``Node right;``        ``Node down;``    ``};`` ` `    ``// returns head pointer of linked list``    ``// constructed from 2D matrix``    ``static` `Node construct(``int` `arr[][], ``int` `i, ``int` `j, ``                                     ``int` `m, ``int` `n) {``         ` `        ``// return if i or j is out of bounds``        ``if` `(i > n - ``1` `|| j > m - ``1``)``            ``return` `null``;`` ` `        ``// create a new node for current i and j``        ``// and recursively allocate its down and``        ``// right pointers``        ``Node temp = ``new` `Node();``        ``temp.data = arr[i][j];``        ``temp.right = construct(arr, i, j + ``1``, m, n);``        ``temp.down = construct(arr, i + ``1``, j, m, n);``        ``return` `temp;``    ``}`` ` `    ``// utility function for displaying``    ``// linked list data``    ``static` `void` `display(Node head) {``         ` `        ``// pointer to move right``        ``Node Rp;`` ` `        ``// pointer to move down``        ``Node Dp = head;`` ` `        ``// loop till node->down is not NULL``        ``while` `(Dp != ``null``) {``            ``Rp = Dp;`` ` `            ``// loop till node->right is not NULL``            ``while` `(Rp != ``null``) {``                ``System.out.print(Rp.data + ``" "``);``                ``Rp = Rp.right;``            ``}``            ``System.out.println();``            ``Dp = Dp.down;``        ``}``    ``}`` ` `    ``// driver program``    ``public` `static` `void` `main(String args[]) {``        ``// 2D matrix``        ``int` `arr[][] = { { ``1``, ``2``, ``3` `}, ``                        ``{ ``4``, ``5``, ``6` `}, ``                       ``{ ``7``, ``8``, ``9` `} };`` ` `        ``int` `m = ``3``, n = ``3``;``        ``Node head = construct(arr, ``0``, ``0``, m, n);``        ``display(head);``    ``}`` ` `}``// This code is contributed by Sumit Ghosh`

## Python3

 `    ``# Python3 program to construct a linked list``# from given 2D matrix``import` `math`` ` `# struct node of linked list``class` `Node: ``    ``def` `__init__(``self``, data): ``        ``self``.data ``=` `data ``        ``self``.right ``=` `None``        ``self``.down ``=` `None`` ` `# returns head pointer of linked list``# constructed from 2D matrix``def` `construct(arr, i, j, m, n):``     ` `    ``# return if i or j is out of bounds``    ``if` `(i > n ``-` `1` `or` `j > m ``-` `1``):``        ``return` `None`` ` `    ``# create a new node for current i and j``    ``# and recursively allocate its down and``    ``# right pointers``    ``temp ``=` `Node(arr[i][j])``    ``temp.data ``=` `arr[i][j]``    ``temp.right ``=` `construct(arr, i, j ``+` `1``, m, n)``    ``temp.down ``=` `construct(arr, i ``+` `1``, j, m, n)``    ``return` `temp`` ` `# utility function for displaying``# linked list data``def` `display(head):``     ` `    ``# pointer to move right``    ``# Rp`` ` `    ``# pointer to move down``    ``Dp ``=` `head`` ` `    ``# loop till node.down is not None``    ``while` `(Dp):``        ``Rp ``=` `Dp`` ` `        ``# loop till node.right is not None``        ``while` `(Rp):``            ``print``(Rp.data, end ``=` `" "``)``            ``Rp ``=` `Rp.right``         ` `        ``print``()``        ``Dp ``=` `Dp.down``     ` `# Driver Code``if` `__name__``=``=``'__main__'``: ``    ``# 2D matrix``    ``arr ``=` `[[ ``1``, ``2``, ``3` `],``           ``[ ``4``, ``5``, ``6` `],``           ``[ ``7``, ``8``, ``9` `]]`` ` `    ``m, n ``=` `3``, ``3``    ``head ``=` `construct(arr, ``0``, ``0``, m, n)``    ``display(head)``     ` `# This code is contributed by AbhiThakur`

## C#

 `// C# program to construct a linked list``// from given 2D matrix``using` `System;``     ` `public` `class` `Linked_list_2D_Matrix``{`` ` `    ``// node of linked list``    ``public` `class` `Node ``    ``{``        ``public` `int` `data;``        ``public` `Node right;``        ``public` `Node down;``    ``};`` ` `    ``// returns head pointer of linked list``    ``// constructed from 2D matrix``    ``static` `Node construct(``int` `[,]arr, ``int` `i, ``int` `j, ``                                    ``int` `m, ``int` `n) ``    ``{``         ` `        ``// return if i or j is out of bounds``        ``if` `(i > n - 1 || j > m - 1)``            ``return` `null``;`` ` `        ``// create a new node for current i and j``        ``// and recursively allocate its down and``        ``// right pointers``        ``Node temp = ``new` `Node();``        ``temp.data = arr[i, j];``        ``temp.right = construct(arr, i, j + 1, m, n);``        ``temp.down = construct(arr, i + 1, j, m, n);``        ``return` `temp;``    ``}`` ` `    ``// utility function for displaying``    ``// linked list data``    ``static` `void` `display(Node head)``    ``{``         ` `        ``// pointer to move right``        ``Node Rp;`` ` `        ``// pointer to move down``        ``Node Dp = head;`` ` `        ``// loop till node->down is not NULL``        ``while` `(Dp != ``null``) ``        ``{``            ``Rp = Dp;`` ` `            ``// loop till node->right is not NULL``            ``while` `(Rp != ``null``) ``            ``{``                ``Console.Write(Rp.data + ``" "``);``                ``Rp = Rp.right;``            ``}``            ``Console.WriteLine();``            ``Dp = Dp.down;``        ``}``    ``}`` ` `    ``// Driver program``    ``public` `static` `void` `Main() ``    ``{``        ``// 2D matrix``        ``int` `[,]arr = { { 1, 2, 3 }, ``                        ``{ 4, 5, 6 }, ``                    ``{ 7, 8, 9 } };`` ` `        ``int` `m = 3, n = 3;``        ``Node head = construct(arr, 0, 0, m, n);``        ``display(head);``    ``}``}`` ` `/* This code contributed by PrinciRaj1992 */`

Output:
```1 2 3
4 5 6
7 8 9
```

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