Java 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.

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
{
    // Head of list
    Node head;

    // 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)
    {
        // Initialize current
        Node current = head;
        while (current != null)
        {
            // Data found
            if (current.data == x)
                return true;
            current = current.next;
        }

        // Data not found
        return false;
    }

    // Driver code
    public static void main(String args[])
    {
        // Start with the empty list
        LinkedList llist = new LinkedList();

        // Use push() to construct 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

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.

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
{
    // Head of list
    Node head;

    // 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 code
    public static void main(String args[])
    {
        // Start with the empty list
        LinkedList llist = new LinkedList();

        // Use push() to construct 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

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!