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Bitonic point in the given linked list

  • Last Updated : 09 Jun, 2021

Given a linked list with distinct elements, the task is to find the bitonic point in the given linked list. If there is no such point then print -1.
Examples: 
 

Input: 1 -> 2 -> 3 -> 4 -> 3 -> 2 -> 1 -> NULL 
Output:
1 -> 2 -> 3 -> 4 is strictly increasing. 
4 -> 3 -> 2 -> 1 -> NULL is strictly decreasing.
Input: 97 -> 98 -> 99 -> 91 -> NULL 
Output: 99 
 

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Approach: A Bitonic Point is a point in bitonic sequence before which elements are strictly increasing and after which elements are strictly decreasing. A Bitonic point doesn’t exist if array is only decreasing or only increasing. So, find the first node such that the value of the node next to it is strictly smaller. Start traversing the linked list from that node onwards and if every other node is strictly smaller than its previous node then the found node was out bitonic sequence else the given linked list doesn’t contain a valid bitonic sequence. Note that an empty list or a list with a single node doesn’t represent a valid bitonic sequence.
Below is the implementation of the above approach: 
 

C++




// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;
 
// Node for linked list
class Node {
public:
    int data;
    Node* next;
};
 
// Function to insert a node at
// the head of the linked list
Node* push(Node** head_ref, int data)
{
    Node* new_node = new Node;
    new_node->data = data;
    new_node->next = (*head_ref);
    (*head_ref) = new_node;
}
 
// Function to return the bitonic
// of the given linked list
int bitonic_point(Node* node)
{
    // If list is empty
    if (node == NULL)
        return -1;
 
    // If list contains only
    // a single node
    if (node->next == NULL)
        return -1;
 
    // Invalid bitonic sequence
    if (node->data > node->next->data)
        return -1;
 
    while (node->next != NULL) {
 
        // If current node is the bitonic point
        if (node->data > node->next->data)
            break;
 
        // Get to the next node in the list
        node = node->next;
    }
 
    int bitonicPoint = node->data;
    // Nodes must be in descending
    // starting from here
    while (node->next != NULL) {
 
        // Out of order node
        if (node->data < node->next->data)
            return -1;
 
        // Get to the next node in the list
        node = node->next;
    }
 
    return bitonicPoint;
}
 
// Driver code
int main()
{
    Node* head = NULL;
 
    push(&head, 100);
    push(&head, 201);
    push(&head, 399);
    push(&head, 490);
    push(&head, 377);
    push(&head, 291);
    push(&head, 100);
 
    cout << bitonic_point(head);
 
    return 0;
}

Java




// Java implementation of the approach
class GFG
{
     
// Node for linked list
static class Node
{
    int data;
    Node next;
};
 
// Function to insert a node at
// the head of the linked list
static Node push(Node head_ref, int data)
{
    Node new_node = new Node();
    new_node.data = data;
    new_node.next = (head_ref);
    (head_ref) = new_node;
    return head_ref;
}
 
// Function to return the bitonic
// of the given linked list
static int bitonic_point(Node node)
{
    // If list is empty
    if (node == null)
        return -1;
 
    // If list contains only
    // a single node
    if (node.next == null)
        return -1;
 
    // Invalid bitonic sequence
    if (node.data > node.next.data)
        return -1;
 
    while (node.next != null)
    {
 
        // If current node is the bitonic point
        if (node.data > node.next.data)
            break;
 
        // Get to the next node in the list
        node = node.next;
    }
 
    int bitonicPoint = node.data;
     
    // Nodes must be in descending
    // starting from here
    while (node.next != null)
    {
 
        // Out of order node
        if (node.data < node.next.data)
            return -1;
 
        // Get to the next node in the list
        node = node.next;
    }
 
    return bitonicPoint;
}
 
// Driver code
public static void main(String args[])
{
    Node head = null;
 
    head=push(head, 100);
    head=push(head, 201);
    head=push(head, 399);
    head=push(head, 490);
    head=push(head, 377);
    head=push(head, 291);
    head=push(head, 100);
 
    System.out.println(bitonic_point(head));
}
}
 
// This code is contributed by Arnab Kundu

Python3




# Python3 implementation of the approach
  
# Node for linked list
class Node:  
    def __init__(self, data):
        self.data = data
        self.next = None
  
# Function to insert a node at
# the head of the linked list
def push(head_ref, data):
 
    new_node = Node(data)
    new_node.next = head_ref
    head_ref = new_node
    return head_ref
     
# Function to return the bitonic
# of the given linked list
def bitonic_point(node):
 
    # If list is empty
    if (node == None):
        return -1;
  
    # If list contains only
    # a single node
    if (node.next == None):
        return -1;
  
    # Invalid bitonic sequence
    if (node.data > node.next.data):
        return -1;
    while (node.next != None):
  
        # If current node is the bitonic point
        if (node.data > node.next.data):
            break;
  
        # Get to the next node in the list
        node = node.next;
    bitonicPoint = node.data;
     
    # Nodes must be in descending
    # starting from here
    while (node.next != None):
  
        # Out of order node
        if (node.data < node.next.data):
            return -1;
  
        # Get to the next node in the list
        node = node.next;
    return bitonicPoint;
  
# Driver code
if __name__=='__main__':
     
    head = None;
  
    head = push(head, 100);
    head = push(head, 201);
    head = push(head, 399);
    head = push(head, 490);
    head = push(head, 377);
    head = push(head, 291);
    head = push(head, 100);
  
    print(bitonic_point(head))
  
# This code is contributed by rutvik_56

C#




// C# implementation of the approach
using System;
     
class GFG
{
     
// Node for linked list
public class Node
{
    public int data;
    public Node next;
};
 
// Function to insert a node at
// the head of the linked list
static Node push(Node head_ref, int data)
{
    Node new_node = new Node();
    new_node.data = data;
    new_node.next = (head_ref);
    (head_ref) = new_node;
    return head_ref;
}
 
// Function to return the bitonic
// of the given linked list
static int bitonic_point(Node node)
{
    // If list is empty
    if (node == null)
        return -1;
 
    // If list contains only
    // a single node
    if (node.next == null)
        return -1;
 
    // Invalid bitonic sequence
    if (node.data > node.next.data)
        return -1;
 
    while (node.next != null)
    {
 
        // If current node is the bitonic point
        if (node.data > node.next.data)
            break;
 
        // Get to the next node in the list
        node = node.next;
    }
 
    int bitonicPoint = node.data;
     
    // Nodes must be in descending
    // starting from here
    while (node.next != null)
    {
 
        // Out of order node
        if (node.data < node.next.data)
            return -1;
 
        // Get to the next node in the list
        node = node.next;
    }
 
    return bitonicPoint;
}
 
// Driver code
public static void Main(String []args)
{
    Node head = null;
 
    head=push(head, 100);
    head=push(head, 201);
    head=push(head, 399);
    head=push(head, 490);
    head=push(head, 377);
    head=push(head, 291);
    head=push(head, 100);
 
    Console.WriteLine(bitonic_point(head));
}
}
 
// This code is contributed by 29AjayKumar

Javascript




<script>
 
// JavaScript implementation of the approach
 
// Node for linked list
 
class Node {
        constructor() {
        this.data = 0;
        this.next = null;
            }
}
 
// Function to insert a node at
// the head of the linked list
function push( head_ref, data)
{
    var new_node = new Node();
    new_node.data = data;
    new_node.next = (head_ref);
    (head_ref) = new_node;
    return head_ref;
}
 
// Function to return the bitonic
// of the given linked list
function bitonic_point( node)
{
    // If list is empty
    if (node == null)
        return -1;
 
    // If list contains only
    // a single node
    if (node.next == null)
        return -1;
 
    // Invalid bitonic sequence
    if (node.data > node.next.data)
        return -1;
 
    while (node.next != null)
    {
 
        // If current node is the bitonic point
        if (node.data > node.next.data)
            break;
 
        // Get to the next node in the list
        node = node.next;
    }
 
    let bitonicPoint = node.data;
     
    // Nodes must be in descending
    // starting from here
    while (node.next != null)
    {
 
        // Out of order node
        if (node.data < node.next.data)
            return -1;
 
        // Get to the next node in the list
        node = node.next;
    }
 
    return bitonicPoint;
}
 
 
 
// Driver Code
 
var head = null;
 
head=push(head, 100);
head=push(head, 201);
head=push(head, 399);
head=push(head, 490);
head=push(head, 377);
head=push(head, 291);
head=push(head, 100);
 
document.write(bitonic_point(head));
     
</script>
Output: 
490

 




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