# C Program For Searching An Element In A Linked List

Write a function that searches a given key ‘x’ in a given singly linked list. The function should return true if x is present in linked list and false otherwise.

`bool search(Node *head, int x)`

For example, if the key to be searched is 15 and linked list is 14->21->11->30->10, then function should return false. If key to be searched is 14, then the function should return true.
Iterative Solution:

```1) Initialize a node pointer, current = head.
2) Do following while current is not NULL
a) current->key is equal to the key being searched return true.
b) current = current->next
3) Return false ```

Following is iterative implementation of above algorithm to search a given key.

## C

 `// Iterative C program to search an ` `// element in linked list` `#include` `#include` `#include`   `// Link list node ` `struct` `Node` `{` `    ``int` `key;` `    ``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_key)` `{` `    ``// Allocate node` `    ``struct` `Node* new_node =` `           ``(``struct` `Node*) ``malloc``(``sizeof``(``struct` `Node));`   `    ``// Put in the key` `    ``new_node->key = new_key;`   `    ``// Link the old list of the new node` `    ``new_node->next = (*head_ref);`   `    ``// Move the head to point to the new node ` `    ``(*head_ref) = new_node;` `}`   `// Checks whether the value x is present` `// in linked list ` `bool` `search(``struct` `Node* head, ``int` `x)` `{` `    ``// Initialize current` `    ``struct` `Node* current = head;  ` `    ``while` `(current != NULL)` `    ``{` `        ``if` `(current->key == x)` `            ``return` `true``;` `        ``current = current->next;` `    ``}` `    ``return` `false``;` `}`   `// Driver code` `int` `main()` `{` `    ``// Start with the empty list ` `    ``struct` `Node* head = NULL;` `    ``int` `x = 21;`   `    ``// Use push() to construct list` `    ``// 14->21->11->30->10 ` `    ``push(&head, 10);` `    ``push(&head, 30);` `    ``push(&head, 11);` `    ``push(&head, 21);` `    ``push(&head, 14);`   `    ``search(head, 21)? ``printf``(``"Yes"``) : ``printf``(``"No"``);` `    ``return` `0;` `}`

Output:

`Yes`

Time Complexity: O(n), where n represents the length of the given linked list.
Auxiliary Space: O(1), no extra space is required, so it is a constant.

Recursive Solution:

```bool search(head, x)
1) If head is NULL, return false.
2) If head's key is same as x, return true;
3) Else return search(head->next, x) ```

Following is the recursive implementation of the above algorithm to search a given key.

## C

 `// Recursive C program to search an ` `// element in linked list` `#include` `#include` `#include` `// Link list node` `struct` `Node` `{` `    ``int` `key;` `    ``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_key)` `{` `    ``// Allocate node` `    ``struct` `Node* new_node =` `           ``(``struct` `Node*) ``malloc``(``sizeof``(``struct` `Node));`   `    ``// Put in the key` `    ``new_node->key = new_key;`   `    ``// Link the old list of the new node` `    ``new_node->next = (*head_ref);`   `    ``// Move the head to point to the new node` `    ``(*head_ref) = new_node;` `}`   `// Checks whether the value x is present` `// in linked list` `bool` `search(``struct` `Node* head, ``int` `x)` `{` `    ``// Base case` `    ``if` `(head == NULL)` `        ``return` `false``;` `    `  `    ``// If key is present in current ` `    ``// node, return true` `    ``if` `(head->key == x)` `        ``return` `true``;`   `    ``// Recur for remaining list` `    ``return` `search(head->next, x);` `}`   `// Driver code` `int` `main()` `{` `    ``// Start with the empty list ` `    ``struct` `Node* head = NULL;` `    ``int` `x = 21;`   `    ``// Use push() to construct list` `    ``// 14->21->11->30->10 ` `    ``push(&head, 10);` `    ``push(&head, 30);` `    ``push(&head, 11);` `    ``push(&head, 21);` `    ``push(&head, 14);`   `    ``search(head, 21)? ``printf``(``"Yes"``) : ``printf``(``"No"``);` `    ``return` `0;` `}`

Output:

`Yes`

Time Complexity: O(n), where n represents the length of the given linked list.
Auxiliary Space: O(n), for recursive call stack where n represents the length of the given linked list.

Please refer complete article on Search an element in a Linked List (Iterative and Recursive) for more details!

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