C++ Linked List Exercises: Find middle element in a single linked list

Last update on December 20 2024 12:23:53 (UTC/GMT +8 hours)

Write a C++ program to find the middle element of a given Linked List.

Test Data:
Original list:
9 7 5 3 1
Middle element of the said list:
5
Original list:
7 5 3 1
Middle element of the said list:
3
Explanation: The second node of the list is returned since it has the values 5 and 3.

Sample Solution:

C++ Code:

#include <iostream> // Including input-output stream header file

using namespace std; // Using standard namespace

// Structure for defining a Node
struct Node {
    int num; // Data field to store a number
    Node *next; // Pointer to the next node
}; // Node constructed

int sz = 0; // Initializing variable to keep track of the size of the linked list

// Function to insert a node at the beginning of the linked list
void insert(Node** head, int num) {
    Node* new_Node = new Node(); // Creating a new node
    new_Node->num = num; // Assigning data to the new node
    new_Node->next = *head; // Pointing the new node to the current head
    *head = new_Node; // Making the new node as the head
    sz++; // Increasing the size of the linked list
}

// Function to find the middle element of a linked list
int get_Middle(Node *head) {
    if (!head) return -1; // If the list is empty, return -1 (no middle element)
    int c = 0; // Counter variable to keep track of the position in the list
    Node *middle = head; // Pointer for the middle element initially set to head
    while (head) {
        if (c % 2 != 0) middle = middle->next; // Update the middle pointer for odd positions
        c++; // Incrementing the counter
        head = head->next; // Move to the next node
    }
    return middle->num; // Return the value of the middle element
}

// Display all nodes in the linked list
void display_all_nodes(Node* node) { 
    while (node != NULL) {
        cout << node->num << " "; // Displaying the data in the current node
        node = node->next; // Move to the next node
    } 
}

int main() {
    Node* head = NULL; // Initializing the head of the linked list as NULL

    insert(&head, 1); // Inserting a node with value 1
    insert(&head, 3); // Inserting a node with value 3
    insert(&head, 5); // Inserting a node with value 5
    insert(&head, 7); // Inserting a node with value 7

    cout << "Original list:\n"; // Displaying message for the original list
    display_all_nodes(head); // Displaying all nodes in the original list

    cout << "\nMiddle element of the said list:"; // Displaying message for the middle element
    cout << "\n" << get_Middle(head) << "\n"; // Finding and displaying the middle element

    cout << "\nOriginal list:\n"; // Displaying message for the updated list after insertion
    insert(&head, 9); // Inserting a node with value 9
    display_all_nodes(head); // Displaying all nodes in the updated list

    cout << "\nMiddle element of the said list:"; // Displaying message for the middle element
    cout << "\n" << get_Middle(head); // Finding and displaying the middle element in the updated list

    cout << endl; // Displaying newline
    return 0; // Returning from the main function
}

Sample Output:

Original list:
7 5 3 1
Middle element of the said list:
3

Original list:
9 7 5 3 1
Middle element of the said list:
5

Flowchart:

CPP Code Editor:

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Previous C++ Exercise: Insert a new node at the end of a Linked List.
Next C++ Exercise: Insert new node at the middle of a Singly Linked List.