Find a peak element in linked list

// C Program
// Find a peak element in linked list
#include <stdio.h>
 //For malloc function
#include <stdlib.h>

//Linked List Node
struct Node
{
    int data;
    struct Node *next;
};
//Create a node of linked list
struct Node *create_node(int data)
{
    //Create dynamic node
    struct Node *node = (struct Node *) malloc(sizeof(struct Node));
    if (node == NULL)
    {
        printf("Memory overflow\n");
    }
    else
    {
        //Set initial node value
        node->data = data;
        node->next = NULL;
    }
    return node;
}
//Add new node at end of linked list 
void insert(struct Node **head, int data)
{
    struct Node *node = create_node(data);
    if ( *head == NULL)
    {
        *head = node;
    }
    else
    {
        struct Node *temp = *head;
        //Find last node
        while (temp->next != NULL)
        {
            temp = temp->next;
        }
        //Add node at last possition
        temp->next = node;
    }
}
//Display linked list element
void display(struct Node *head)
{
    if (head == NULL)
    {
        printf("\nEmpty linked list\n");
        return;
    }
    struct Node *temp = head;
    printf("\n Linked List : ");
    //iterating linked list elements
    while (temp != NULL)
    {
        if(temp != head)
        {
            printf(" →");
        }
        
        printf(" %d", temp->data);
        
        
        //visit to next node
        temp = temp->next;
    }
    printf(" → NULL");
}

//Check that left side smaller element exist or not
int is_left_side_smaller(struct Node*start,struct Node*last)
{

    while(start != NULL && start != last)
    {
        if(start->data < last->data)
        {
            return 1;
        }
        //visit to next node
        start = start->next;
    }
    return 0;
}
//Check that right side smaller element exist or not
int is_right_side_smaller(struct Node*start)
{
    struct Node*temp = start->next;

    while(temp != NULL)
    {
        if(temp->data < start->data)
        {
            return 1;
        }
        temp = temp->next;
    }
    return 0;
}


//Find first peak node in given linked list
void peak_node(struct Node *head)
{

    //Display linked list elements
    display(head);

    struct Node *result = NULL;

    if(head!=NULL && head->next!=NULL)
    {
        //Define some auxiliary variable
        struct Node *current = head->next;

        //iterating linked list elements
        while (current != NULL && result == NULL  && current->next != NULL)
        {
          
            if(is_left_side_smaller(head,current) 
                && is_right_side_smaller(current))
            {
                result = current;
            }
            //visit to next node
            current = current->next;
        }

    }
    if (result == NULL)
    {
        printf("\n Peak node : None\n");
    }
    else
    {
        printf("\n Peak node : %d\n", result->data);
    }
}
int main()
{
    //Define few empty  linked list
    struct Node *list1 = NULL;
    struct Node *list2 = NULL;
    struct Node *list3 = NULL;


    //Add node in first linked list
    // 1 → 5 → 6 → 2 → NULL
    insert( &list1, 1);
    insert( &list1, 5);
    insert( &list1, 6);
    insert( &list1, 2);
 

    peak_node(list1);
    //Add node in second linked list
    //  4 → 6 → 5 → 10 → 3 → NULL
    insert( &list2, 4);
    insert( &list2, 6);
    insert( &list2, 5);
    insert( &list2, 10);
    insert( &list2, 3);
    
    peak_node(list2);
    //Add node in third linked list
    //   1 → 2 → 4 → NULL
    insert( &list3, 1);
    insert( &list3, 2);
    insert( &list3, 4);
    peak_node(list3);
    return 0;
}

Output

 Linked List :  1 → 5 → 6 → 2 → NULL
 Peak node : 5

 Linked List :  4 → 6 → 5 → 10 → 3 → NULL
 Peak node : 6

 Linked List :  1 → 2 → 4 → NULL
 Peak node : None