Search an element in a Linked List (Iterative and Recursive)

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

2) Initialize a node pointer, current = head.
3) Do following while current is not NULL
    a) current->key is equal to the key being searched return true.
    b) current = current->next
4) 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<stdio.h> 
#include<stdlib.h> 
#include<stdbool.h 
  
/* 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 off 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) 
{ 
    struct Node* current = head;  // Initialize current 
    while (current != NULL) 
    { 
        if (current->key == x) 
            return true; 
        current = current->next; 
    } 
    return false; 
} 
  
/* Driver program to test count function*/
int main() 
{ 
    /* Start with the empty list */
    struct Node* head = NULL; 
    int x = 21; 
  
    /* Use push() to construct below 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; 
} 

Java

// Iterative Java program to search an element 
// in linked list 
  
//Node class 
class Node 
{ 
    int data; 
    Node next; 
    Node(int d) 
    { 
        data = d; 
        next = null; 
    } 
} 
  
//Linked list class 
class LinkedList 
{ 
    Node head;    //Head of list 
  
    //Inserts a new node at the front of the list 
    public void push(int new_data) 
    { 
        //Allocate new node and putting data 
        Node new_node = new Node(new_data); 
  
        //Make next of new node as head 
        new_node.next = head; 
  
        //Move the head to point to new Node 
        head = new_node; 
    } 
  
    //Checks whether the value x is present in linked list 
    public boolean search(Node head, int x) 
    { 
        Node current = head;    //Initialize current 
        while (current != null) 
        { 
            if (current.data == x) 
                return true;    //data found 
            current = current.next; 
        } 
        return false;    //data not found 
    } 
  
    //Driver function to test the above functions 
    public static void main(String args[]) 
    { 
  
        //Start with the empty list 
        LinkedList llist = new LinkedList(); 
  
        /*Use push() to construct below list 
        14->21->11->30->10  */
        llist.push(10); 
        llist.push(30); 
        llist.push(11); 
        llist.push(21); 
        llist.push(14); 
  
        if (llist.search(llist.head, 21)) 
            System.out.println("Yes"); 
        else
            System.out.println("No"); 
    } 
} 
// This code is contributed by Pratik Agarwal 

Python

# Iterative Python program to search an element 
# in linked list 
  
# Node class 
class Node: 
      
    # Function to initialise the node object 
    def __init__(self, data): 
        self.data = data # Assign data 
        self.next = None # Initialize next as null 
  
# Linked List class 
class LinkedList: 
    def __init__(self): 
        self.head = None # Initialize head as None 
  
    # This function insert a new node at the 
    # beginning of the linked list 
    def push(self, new_data): 
      
        # Create a new Node 
        new_node = Node(new_data) 
  
        # 3. Make next of new Node as head 
        new_node.next = self.head 
  
        # 4. Move the head to point to new Node 
        self.head = new_node 
  
    # This Function checks whether the value 
    # x present in the linked list  
    def search(self, x): 
  
        # Initialize current to head 
        current = self.head 
  
        # loop till current not equal to None 
        while current != None: 
            if current.data == x: 
                return True # data found 
              
            current = current.next
          
        return False # Data Not found 
  
  
# Code execution starts here 
if __name__ == '__main__': 
  
    # Start with the empty list 
    llist = LinkedList() 
  
    ''' Use push() to construct below list 
        14->21->11->30->10 '''
    llist.push(10); 
    llist.push(30); 
    llist.push(11); 
    llist.push(21); 
    llist.push(14); 
  
    if llist.search(21): 
        print("Yes") 
    else: 
        print("No") 
  
# This code is contributed by Ravi Shankar 

Output:

Yes

Recursive Solution

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

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

C

// Recursive C program to search an element in linked list 
#include<stdio.h> 
#include<stdlib.h> 
#include<stdbool.h> 
/* 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 off 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 program to test count function*/
int main() 
{ 
    /* Start with the empty list */
    struct Node* head = NULL; 
    int x = 21; 
  
    /* Use push() to construct below 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; 
} 

Java

// Recursive Java program to search an element 
// in linked list 
  
  
// Node class 
class Node 
{ 
    int data; 
    Node next; 
    Node(int d) 
    { 
        data = d; 
        next = null; 
    } 
} 
  
// Linked list class 
class LinkedList 
{ 
    Node head;    //Head of list 
  
    //Inserts a new node at the front of the list 
    public void push(int new_data) 
    { 
        //Allocate new node and putting data 
        Node new_node = new Node(new_data); 
  
        //Make next of new node as head 
        new_node.next = head; 
  
        //Move the head to point to new Node 
        head = new_node; 
    } 
  
    // Checks whether the value x is present 
    // in linked list 
    public boolean search(Node head, int x) 
    { 
        // Base case 
        if (head == null) 
            return false; 
  
        // If key is present in current node, 
        // return true 
        if (head.data == x) 
            return true; 
  
        // Recur for remaining list 
        return search(head.next, x); 
    } 
  
    // Driver function to test the above functions 
    public static void main(String args[]) 
    { 
        // Start with the empty list 
        LinkedList llist = new LinkedList(); 
  
        /* Use push() to construct below list 
           14->21->11->30->10  */
        llist.push(10); 
        llist.push(30); 
        llist.push(11); 
        llist.push(21); 
        llist.push(14); 
  
        if (llist.search(llist.head, 21)) 
            System.out.println("Yes"); 
        else
            System.out.println("No"); 
    } 
} 
// This code is contributed by Pratik Agarwal 

Output:

Yes

Python

# Recursive Python program to  
# search an element in linked list 
  
# Node class 
class Node: 
      
    # Function to initialise  
    # the node object 
    def __init__(self, data): 
        self.data = data # Assign data 
        self.next = None # Initialize next as null 
  
class LinkedList: 
      
    def __init__(self): 
        self.head = None # Initialize head as None 
  
    # This function insert a new node at  
    # the beginning of the linked list 
    def push(self, new_data): 
      
        # Create a new Node 
        new_node = Node(new_data) 
  
        # Make next of new Node as head 
        new_node.next = self.head 
  
        # Move the head to  
        # point to new Node 
        self.head = new_node 
      
      
    # Checks whether the value key  
    # is present in linked list  
    def search(self, li, key): 
          
        # Base case 
        if(not li): 
            return False
          
        # If key is present in  
        # current node, return true 
        if(li.data == key): 
            return True
          
        # Recur for remaining list 
        return self.search(li.next, key) 
      
# Driver Code             
if __name__=='__main__': 
  
    li = LinkedList() 
      
    li.push(1) 
    li.push(2) 
    li.push(3) 
    li.push(4) 
      
    key = 4
      
    if li.search(li.head,key): 
        print("Yes") 
    else: 
        print("No") 
      
# This code is contributed 
# by Manoj Sharma 

Output:

Yes

This article is contributed by Ravi. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above

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