Searching an Element in a Linked List using C++

To search an element in a linked list, we must iterate through the complete list, compare each node with the desired data, and keep searching until a match is obtained. Because a Linked List does not provide random access, we must start the search from the first node.

We are given a linked list of integers and an integer key. We need to find if this key exists in our linked list or not. We can do a simple linear search in the linked list and find the key. If present, we can return "Yes"; otherwise, "No"

Let us look at some input-output scenarios −

We have taken a list where we need to find whether the element is present in that list and get the output accordingly with the provided key as 3 −

Input Data: [ 10, 4, 5, 4, 10, 1, 3, 5]
Output: Yes

Let’s consider another scenario with the key provided as 5 −

Input Data: [ 1, 4, 9, 4, 10, 1, 3, 6]
Output: No

Algorithm (Steps)

Following are the Algorithm/steps to be followed to perform the desired task −

• Set up the head as null.

• Add few items to the Linked List

• Get the user's input for the item to be searched for.

• Linearly traverse the Linked List from head to end until you reach the null node.

• Check each node to see if the data value matches the item to be searched.

• Return the index of the node where the data was found. If not found, go to the next node.

Example

For example, let's have a linked list such as "52->4651->42->5->12587->874->8->null" and its key is 12587. The C++ program to implement the example is given below −

#include <iostream>
using namespace std;
class Node {
   public:
   int val;
   Node* next;
   Node(int val) {
      this->val = val;
      next = NULL;
   }
};
void solve(Node* head, int key) {
   while(head) {
      if(head->val == key) {
         cout << "Yes";
         return;
      }
      head = head->next;
   }
   cout << "No";
}
int main() {
   Node* head = new Node(52);
   head->next = new Node(4651);
   head->next->next = new Node(42);
   head->next->next->next = new Node(5);
   head->next->next->next->next = new Node(12587);
   head->next->next->next->next->next = new Node(874);
   head->next->next->next->next->next->next = new Node(8);
   solve(head, 12587);
   return 0;
}

Output

Yes

Example

Now we will use the recursive approach to solve the same problem −

#include <iostream>
using namespace std;
class Node {
   public:
   int val;
   Node* next;
   Node(int val) {
      this->val = val;
      next = NULL;
   }
};
void solve(Node* head, int key) {
   if(head == NULL) {
      cout << "No";
   } else if(head->val == key) {
      cout << "Yes";
   } else {
      solve(head->next, key);
   }
}
int main() {
   Node* head = new Node(52);
   head->next = new Node(4651);
   head->next->next = new Node(42);
   head->next->next->next = new Node(5);
   head->next->next->next->next = new Node(12587);
   head->next->next->next->next->next = new Node(874);
   head->next->next->next->next->next->next = new Node(8);
   solve(head, 12587);
   return 0;
}

Output

Yes

Conclusion

The time complexity is O(n). We have used an iterative approach to solve this problem. Try this problem with a recursive approach.

Prateek Jangid

Updated on: 10-Aug-2022

4K+ Views

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