# Create linked list from a given array

Given an array arr[] of size N. The task is to create linked list from the given array.

Examples:

```Input : arr[]={1, 2, 3, 4, 5}
Output : 1->2->3->4->5

Input :arr[]={10, 11, 12, 13, 14}
Output : 10->11->12->13->14
```

Simple Approach: For each element of an array arr[] we create a node in a linked list and insert it at the end.

## C++

 `#include ` `using` `namespace` `std; ` ` `  `// Representation of a node ` `struct` `Node { ` `    ``int` `data; ` `    ``Node* next; ` `}; ` ` `  `// Function to insert node ` `void` `insert(Node** root, ``int` `item) ` `{ ` `    ``Node* temp = ``new` `Node; ` `    ``Node* ptr; ` `    ``temp->data = item; ` `    ``temp->next = NULL; ` ` `  `    ``if` `(*root == NULL) ` `        ``*root = temp; ` `    ``else` `{ ` `        ``ptr = *root; ` `        ``while` `(ptr->next != NULL) ` `            ``ptr = ptr->next; ` `        ``ptr->next = temp; ` `    ``} ` `} ` ` `  `void` `display(Node* root) ` `{ ` `    ``while` `(root != NULL) { ` `        ``cout << root->data << ``" "``; ` `        ``root = root->next; ` `    ``} ` `} ` ` `  `Node *arrayToList(``int` `arr[], ``int` `n) ` `{ ` `    ``Node *root = NULL; ` `    ``for` `(``int` `i = 0; i < n; i++) ` `        ``insert(&root, arr[i]); ` `   ``return` `root; ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``int` `arr[] = { 1, 2, 3, 4, 5 }; ` `    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr[0]); ` `    ``Node* root = arrayToList(arr, n); ` `    ``display(root); ` `    ``return` `0; ` `}`

## Java

 `// Java implementation of the approach ` `import` `java.util.*; ` `class` `GFG ` `{  ` `     `  `// Representation of a node ` `static` `class` `Node  ` `{ ` `    ``int` `data; ` `    ``Node next; ` `}; ` ` `  `// Function to insert node ` `static` `Node insert(Node root, ``int` `item) ` `{ ` `    ``Node temp = ``new` `Node(); ` `    ``Node ptr; ` `    ``temp.data = item; ` `    ``temp.next = ``null``; ` ` `  `    ``if` `(root == ``null``) ` `        ``root = temp; ` `    ``else`  `    ``{ ` `        ``ptr = root; ` `        ``while` `(ptr.next != ``null``) ` `            ``ptr = ptr.next; ` `        ``ptr.next = temp; ` `    ``} ` `    ``return` `root; ` `} ` ` `  `static` `void` `display(Node root) ` `{ ` `    ``while` `(root != ``null``)  ` `    ``{ ` `        ``System.out.print( root.data + ``" "``); ` `        ``root = root.next; ` `    ``} ` `} ` ` `  `static` `Node arrayToList(``int` `arr[], ``int` `n) ` `{ ` `    ``Node root = ``null``; ` `    ``for` `(``int` `i = ``0``; i < n; i++) ` `        ``root = insert(root, arr[i]); ` `    ``return` `root; ` `} ` ` `  `// Driver code ` `public` `static` `void` `main(String args[]) ` `{ ` `    ``int` `arr[] = { ``1``, ``2``, ``3``, ``4``, ``5` `}; ` `    ``int` `n = arr.length; ` `    ``Node root = arrayToList(arr, n); ` `    ``display(root); ` `} ` `} ` ` `  `// This code is contributed by Arnab Kundu `

## Python3

 `# Python3 implementation of the approach  ` `import` `math ` ` `  `# Representation of a node ` `class` `Node:  ` `    ``def` `__init__(``self``, data):  ` `        ``self``.data ``=` `data  ` `        ``self``.``next` `=` `None` ` `  `# Function to insert node ` `def` `insert(root, item): ` `    ``temp ``=` `Node(item) ` `     `  `    ``if` `(root ``=``=` `None``): ` `        ``root ``=` `temp ` `    ``else` `: ` `        ``ptr ``=` `root ` `        ``while` `(ptr.``next` `!``=` `None``): ` `            ``ptr ``=` `ptr.``next` `        ``ptr.``next` `=` `temp ` `     `  `    ``return` `root ` ` `  `def` `display(root): ` `    ``while` `(root !``=` `None``) : ` `        ``print``(root.data, end ``=` `" "``) ` `        ``root ``=` `root.``next` `         `  `def` `arrayToList(arr, n): ` `    ``root ``=` `None` `    ``for` `i ``in` `range``(``0``, n, ``1``): ` `        ``root ``=` `insert(root, arr[i]) ` `     `  `    ``return` `root ` ` `  `# Driver code ` `if` `__name__``=``=``'__main__'``:  ` `    ``arr ``=` `[``1``, ``2``, ``3``, ``4``, ``5``] ` `    ``n ``=` `len``(arr) ` `    ``root ``=` `arrayToList(arr, n) ` `    ``display(root) ` `     `  `# This code is contributed by Srathore `

## C#

 `// C# implementation of the above approach  ` `using` `System;  ` `     `  `class` `GFG ` `{  ` `     `  `// Representation of a node ` `public` `class` `Node  ` `{ ` `    ``public` `int` `data; ` `    ``public` `Node next; ` `}; ` ` `  `// Function to insert node ` `static` `Node insert(Node root, ``int` `item) ` `{ ` `    ``Node temp = ``new` `Node(); ` `    ``Node ptr; ` `    ``temp.data = item; ` `    ``temp.next = ``null``; ` ` `  `    ``if` `(root == ``null``) ` `        ``root = temp; ` `    ``else` `    ``{ ` `        ``ptr = root; ` `        ``while` `(ptr.next != ``null``) ` `            ``ptr = ptr.next; ` `        ``ptr.next = temp; ` `    ``} ` `    ``return` `root; ` `} ` ` `  `static` `void` `display(Node root) ` `{ ` `    ``while` `(root != ``null``)  ` `    ``{ ` `        ``Console.Write(root.data + ``" "``); ` `        ``root = root.next; ` `    ``} ` `} ` ` `  `static` `Node arrayToList(``int` `[]arr, ``int` `n) ` `{ ` `    ``Node root = ``null``; ` `    ``for` `(``int` `i = 0; i < n; i++) ` `        ``root = insert(root, arr[i]); ` `    ``return` `root; ` `} ` ` `  `// Driver code ` `public` `static` `void` `Main(String []args) ` `{ ` `    ``int` `[]arr = { 1, 2, 3, 4, 5 }; ` `    ``int` `n = arr.Length; ` `    ``Node root = arrayToList(arr, n); ` `    ``display(root); ` `} ` `} ` ` `  `// This code is contributed by PrinciRaj1992  `

Output:

```1 2 3 4 5
```

Time Complexity : O(n*n)

Efficient Approach: We traverse array from end and insert every element at the beginning of the list.

## C++

 `#include ` `using` `namespace` `std; ` ` `  `// Representation of a node ` `struct` `Node { ` `    ``int` `data; ` `    ``Node* next; ` `}; ` ` `  `// Function to insert node ` `void` `insert(Node** root, ``int` `item) ` `{ ` `    ``Node* temp = ``new` `Node; ` `    ``temp->data = item; ` `    ``temp->next = *root; ` `    ``*root = temp; ` `} ` ` `  `void` `display(Node* root) ` `{ ` `    ``while` `(root != NULL) { ` `        ``cout << root->data << ``" "``; ` `        ``root = root->next; ` `    ``} ` `} ` ` `  `Node *arrayToList(``int` `arr[], ``int` `n) ` `{ ` `    ``Node *root = NULL; ` `    ``for` `(``int` `i = n-1; i >= 0 ; i--) ` `        ``insert(&root, arr[i]); ` `    ``return` `root; ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``int` `arr[] = { 1, 2, 3, 4, 5 }; ` `    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr[0]); ` `    ``Node* root = arrayToList(arr, n); ` `    ``display(root); ` `    ``return` `0; ` `}`

## Java

 `// Java program to print level order traversal ` `// in spiral form using one queue and one stack. ` `import` `java.util.*; ` `class` `GFG  ` `{  ` ` `  `// Representation of a node ` `static` `class` `Node  ` `{ ` `    ``int` `data; ` `    ``Node next; ` `}; ` `static` `Node root;  ` ` `  `// Function to insert node ` `static` `Node insert(Node root, ``int` `item) ` `{ ` `    ``Node temp = ``new` `Node(); ` `    ``temp.data = item; ` `    ``temp.next = root; ` `    ``root = temp; ` `    ``return` `root; ` `} ` ` `  `static` `void` `display(Node root) ` `{ ` `    ``while` `(root != ``null``)  ` `    ``{ ` `        ``System.out.print(root.data + ``" "``); ` `        ``root = root.next; ` `    ``} ` `} ` ` `  `static` `Node arrayToList(``int` `arr[], ``int` `n) ` `{ ` `    ``root = ``null``; ` `    ``for` `(``int` `i = n - ``1``; i >= ``0` `; i--) ` `        ``root = insert(root, arr[i]); ` `    ``return` `root; ` `} ` ` `  `// Driver code ` `public` `static` `void` `main(String[] args) ` `{ ` `    ``int` `arr[] = { ``1``, ``2``, ``3``, ``4``, ``5` `}; ` `    ``int` `n = arr.length; ` `    ``Node root = arrayToList(arr, n); ` `    ``display(root); ` `} ` `} ` ` `  `// This code is contributed by Princi Singh `

## Python3

 `# Python3 program to prlevel order traversal  ` `# in spiral form using one queue and one stack.  ` ` `  `# Representation of a Node  ` `class` `Node:  ` `    ``def` `__init__(``self``, data):  ` `        ``self``.data ``=` `data  ` `        ``self``.``next` `=` `next` ` `  `# Function to insert Node  ` `def` `insert(root, item):  ` `    ``temp ``=` `Node(``0``)  ` `    ``temp.data ``=` `item  ` `    ``temp.``next` `=` `root  ` `    ``root ``=` `temp ` `    ``return` `root  ` ` `  `def` `display(root):  ` `    ``while` `(root !``=` `None``):  ` `        ``print``(root.data, end``=``" "``)  ` `        ``root ``=` `root.``next`  ` `  `def` `arrayToList(arr, n):  ` `    ``root ``=` `None`  `    ``for` `i ``in` `range``(n ``-` `1``, ``-``1``, ``-``1``):  ` `        ``root ``=` `insert(root, arr[i]) ` `    ``return` `root  ` ` `  `# Driver code  ` `if` `__name__ ``=``=` `'__main__'``:  ` `    ``arr ``=` `[``1``, ``2``, ``3``, ``4``, ``5``];  ` `    ``n ``=` `len``(arr)  ` `    ``root ``=` `arrayToList(arr, n);  ` `    ``display(root)  ` ` `  `# This code is contributed by 29AjayKumar  `

## C#

 `// C# program to print level order traversal ` `// in spiral form using one queue and one stack. ` `using` `System; ` `     `  `class` `GFG  ` `{  ` ` `  `// Representation of a node ` `public` `class` `Node  ` `{ ` `    ``public` `int` `data; ` `    ``public` `Node next; ` `}; ` `static` `Node root;  ` ` `  `// Function to insert node ` `static` `Node insert(Node root, ``int` `item) ` `{ ` `    ``Node temp = ``new` `Node(); ` `    ``temp.data = item; ` `    ``temp.next = root; ` `    ``root = temp; ` `    ``return` `root; ` `} ` ` `  `static` `void` `display(Node root) ` `{ ` `    ``while` `(root != ``null``)  ` `    ``{ ` `        ``Console.Write(root.data + ``" "``); ` `        ``root = root.next; ` `    ``} ` `} ` ` `  `static` `Node arrayToList(``int` `[]arr, ``int` `n) ` `{ ` `    ``root = ``null``; ` `    ``for` `(``int` `i = n - 1; i >= 0 ; i--) ` `        ``root = insert(root, arr[i]); ` `    ``return` `root; ` `} ` ` `  `// Driver code ` `public` `static` `void` `Main(String[] args) ` `{ ` `    ``int` `[]arr = { 1, 2, 3, 4, 5 }; ` `    ``int` `n = arr.Length; ` `    ``Node root = arrayToList(arr, n); ` `    ``display(root); ` `} ` `} ` ` `  `// This code is contributed by Rajput-Ji `

Output:

```1 2 3 4 5
```

Time Complexity : O(n)

Alternate Efficient Solution is maintain tail pointer, traverse array elements from left to right, insert at tail and update tail after insertion.

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