Friday, 07 July 2017 03:58

## Write a function to get Nth node in a Linked List

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Write a GetNth() function that takes a linked list and an integer index and returns the data value stored in the node at that index position.

Example:

```Input:  1->10->30->14,  index = 2
Output: 30
The node at index 2 is 30```

Algorithm:

```1. Initialize count = 0
2. Loop through the link list
a. if count is equal to the passed index then return current
node
b. Increment count
c. change current to point to next of the current.
```

Implementation:

`// C program to find n'th node in linked list`
`#include <stdio.h>`
`#include <stdlib.h>`
`#include <assert.h>`

`/* Link list node */`
`struct` `Node`
`{`
`    ``int` `data;`
`    ``struct` `Node* next;`
`};`

`/* Given a reference (pointer to pointer) to the head`
`    ``of a list and an int, push a new node on the front`
`    ``of the list. */`
`void` `push(``struct` `Node** head_ref, ``int` `new_data)`
`{`
`    ``/* allocate node */`
`    ``struct` `Node* new_node =`
`            ``(``struct` `Node*) ``malloc``(``sizeof``(``struct` `Node));`

`    ``/* put in the data  */`
`    ``new_node->data  = new_data;`
`  `
`    ``/* link the old list off the new node */`
`    ``new_node->next = (*head_ref);`
`  `
`    ``/* move the head to point to the new node */`
`    ``(*head_ref)    = new_node;`
`}`

`/* Takes head pointer of the linked list and index`
`    ``as arguments and return data at index*/`
`int` `GetNth(``struct` `Node* head, ``int` `index)`
`{`
`    ``struct` `Node* current = head;`
`    ``int` `count = 0; ``/* the index of the node we're currently`
`                  ``looking at */`
`    ``while` `(current != NULL)`
`    ``{`
`       ``if` `(count == index)`
`          ``return``(current->data);`
`       ``count++;`
`       ``current = current->next;`
`    ``}`
`  `
`    ``/* if we get to this line, the caller was asking`
`       ``for a non-existent element so we assert fail */`
`    ``assert``(0);              `
`}`

`/* Drier program to test above function*/`
`int` `main()`
`{`
`    ``/* Start with the empty list */`
`    ``struct` `Node* head = NULL;`
`  `
`    ``/* Use push() to construct below list`
`     ``1->12->1->4->1  */`
`    ``push(&head, 1);`
`    ``push(&head, 4);`
`    ``push(&head, 1);`
`    ``push(&head, 12);`
`    ``push(&head, 1);  `
`  `
`    ``/* Check the count function */`
`    ``printf``(``"Element at index 3 is %d"``, GetNth(head, 3));  `
`    ``getchar``();`

`}`
`Output:`
`Element at index 3 is 4` 