# Find the Second Largest Element in a Linked List

Given a Linked list of integer data. The task is to write a program that efficiently finds the second largest element present in the Linked List.

Examples:

```Input : List = 12 -> 35 -> 1 -> 10 -> 34 -> 1
Output : The second largest element is 34.

Input : List = 10 -> 5 -> 10
Output : The second largest element is 5.
```

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

A Simple Solution will be to first sort the linked list in descending order and then print the second element from the sorted linked list. The time complexity of this solution is O(nlogn).

A Better Solution is to traverse the Linked list twice. In the first traversal find the maximum element. In the second traversal find the greatest element less than the element obtained in first traversal. The time complexity of this solution is O(n).

A more Efficient Solution can be to find the second largest element in a single traversal.
Below is the complete algorithm for doing this:

```1) Initialize two variables first and second to INT_MIN as,
first = second = INT_MIN
2) Start traversing the Linked List,
a) If the current element in Linked List say list[i] is greater
than first. Then update first and second as,
second = first
first = list[i]
b) If the current element is in between first and second,
then update second to store the value of current variable as
second = list[i]
3) Return the value stored in second node.
```

Below is the implementation of the above approach:

## C++

 `// C++ program to print second largest ` `// value in a linked list ` `#include ` `#include ` ` `  `using` `namespace` `std; ` ` `  `// A linked list node ` `struct` `Node { ` `    ``int` `data; ` `    ``struct` `Node* next; ` `}; ` ` `  `// Function to add a node at the ` `// beginning of Linked List ` `void` `push(``struct` `Node** head_ref, ``int` `new_data) ` `{ ` `    ``/* allocate node */` `    ``struct` `Node* new_node = (``struct` `Node*)``malloc``(``sizeof``(``struct` `Node)); ` ` `  `    ``/* put in the data */` `    ``new_node->data = new_data; ` ` `  `    ``/* link the old list off the new node */` `    ``new_node->next = (*head_ref); ` ` `  `    ``/* move the head to point to the new node */` `    ``(*head_ref) = new_node; ` `} ` ` `  `// Function to count size of list ` `int` `listSize(``struct` `Node* node) ` `{ ` `    ``int` `count = 0; ` ` `  `    ``while` `(node != NULL) { ` `        ``count++; ` ` `  `        ``node = node->next; ` `    ``} ` ` `  `    ``return` `count; ` `} ` ` `  `// Function to print the second ` `// largest element ` `void` `print2largest(``struct` `Node* head) ` `{ ` `    ``int` `i, first, second; ` ` `  `    ``int` `list_size = listSize(head); ` ` `  `    ``/* There should be atleast two elements */` `    ``if` `(list_size < 2) { ` `        ``cout << ``"Invalid Input"``; ` `        ``return``; ` `    ``} ` ` `  `    ``first = second = INT_MIN; ` ` `  `    ``struct` `Node* temp = head; ` ` `  `    ``while` `(temp != NULL) { ` `        ``if` `(temp->data > first) { ` `            ``second = first; ` `            ``first = temp->data; ` `        ``} ` ` `  `        ``// If current node's data is in between ` `        ``// first and second then update second ` `        ``else` `if` `(temp->data > second && temp->data != first) ` `            ``second = temp->data; ` ` `  `        ``temp = temp->next; ` `    ``} ` ` `  `    ``if` `(second == INT_MIN) ` `        ``cout << ``"There is no second largest element\n"``; ` `    ``else` `        ``cout << ``"The second largest element is "` `<< second; ` `} ` ` `  `// Driver program to test above function ` `int` `main() ` `{ ` `    ``struct` `Node* start = NULL; ` ` `  `    ``/* The constructed linked list is:  ` `     ``12 -> 35 -> 1 -> 10 -> 34 -> 1 */` `    ``push(&start, 1); ` `    ``push(&start, 34); ` `    ``push(&start, 10); ` `    ``push(&start, 1); ` `    ``push(&start, 35); ` `    ``push(&start, 12); ` ` `  `    ``print2largest(start); ` ` `  `    ``return` `0; ` `} `

## Java

 `// Java program to print second largest  ` `// value in a linked list  ` `class` `GFG ` `{ ` `     `  `// A linked list node  ` `static` `class` `Node  ` `{  ` `    ``int` `data;  ` `    ``Node next;  ` `};  ` ` `  `// Function to add a node at the  ` `// beginning of Linked List  ` `static` `Node push( Node head_ref, ``int` `new_data)  ` `{  ` `    ``// allocate node / ` `    ``Node new_node = ``new` `Node();  ` ` `  `    ``// put in the data / ` `    ``new_node.data = new_data;  ` ` `  `    ``// link the old list off the new node / ` `    ``new_node.next = (head_ref);  ` ` `  `    ``// move the head to point to the new node / ` `    ``(head_ref) = new_node;  ` `    ``return` `head_ref; ` `}  ` ` `  `// Function to count size of list  ` `static` `int` `listSize( Node node)  ` `{  ` `    ``int` `count = ``0``;  ` ` `  `    ``while` `(node != ``null``) ` `    ``{  ` `        ``count++;  ` ` `  `        ``node = node.next;  ` `    ``}  ` ` `  `    ``return` `count;  ` `}  ` ` `  `// Function to print the second  ` `// largest element  ` `static` `void` `print2largest( Node head)  ` `{  ` `    ``int` `i, first, second;  ` ` `  `    ``int` `list_size = listSize(head);  ` ` `  `    ``// There should be atleast two elements / ` `    ``if` `(list_size < ``2``)  ` `    ``{  ` `        ``System.out.print(``"Invalid Input"``);  ` `        ``return``;  ` `    ``}  ` ` `  `    ``first = second = Integer.MIN_VALUE;  ` ` `  `    ``Node temp = head;  ` ` `  `    ``while` `(temp != ``null``) ` `    ``{  ` `        ``if` `(temp.data > first)  ` `        ``{  ` `            ``second = first;  ` `            ``first = temp.data;  ` `        ``}  ` ` `  `        ``// If current node's data is in between  ` `        ``// first and second then update second  ` `        ``else` `if` `(temp.data > second && temp.data != first)  ` `            ``second = temp.data;  ` ` `  `        ``temp = temp.next;  ` `    ``}  ` ` `  `    ``if` `(second == Integer.MIN_VALUE)  ` `        ``System.out.print( ``"There is no second largest element\n"``);  ` `    ``else` `        ``System.out.print (``"The second largest element is "` `+ second);  ` `}  ` ` `  `// Driver program to test above function  ` `public` `static` `void` `main(String args[]) ` `{  ` `    ``Node start = ``null``;  ` ` `  `    ``// The constructed linked list is:  ` `    ``//12 . 35 . 1 . 10 . 34 . 1  ` `    ``start=push(start, ``1``);  ` `    ``start=push(start, ``34``);  ` `    ``start=push(start, ``10``);  ` `    ``start=push(start, ``1``);  ` `    ``start=push(start, ``35``);  ` `    ``start=push(start, ``12``);  ` ` `  `    ``print2largest(start);  ` `} ` `}  ` ` `  `// This code is contributed by Arnab Kundu `

## Python3

 `# Python3 program to print second largest  ` `# value in a linked list  ` ` `  `# A linked list node  ` `class` `Node : ` `    ``def` `__init__(``self``): ` `        ``self``.data ``=` `0` `        ``self``.``next` `=` `None` ` `  `# Function to add a node at the  ` `# beginning of Linked List  ` `def` `push( head_ref, new_data) : ` ` `  `    ``# allocate node / ` `    ``new_node ``=` `Node()  ` ` `  `    ``# put in the data / ` `    ``new_node.data ``=` `new_data  ` ` `  `    ``# link the old list off the new node / ` `    ``new_node.``next` `=` `(head_ref)  ` ` `  `    ``# move the head to point to the new node / ` `    ``(head_ref) ``=` `new_node  ` `    ``return` `head_ref ` ` `  `# Function to count size of list  ` `def` `listSize( node):  ` ` `  `    ``count ``=` `0` `    ``while` `(node !``=` `None``): ` `        ``count ``=` `count ``+` `1` ` `  `        ``node ``=` `node.``next` `     `  `    ``return` `count  ` ` `  `# Function to print the second  ` `# largest element  ` `def` `print2largest( head):  ` ` `  `    ``i ``=` `0` `    ``first ``=` `0` `    ``second ``=` `0` ` `  `    ``list_size ``=` `listSize(head)  ` ` `  `    ``# There should be atleast two elements / ` `    ``if` `(list_size < ``2``) : ` `     `  `        ``print``(``"Invalid Input"``)  ` `        ``return` ` `  `    ``first ``=` `second ``=` `-``323767` `    ``temp ``=` `head  ` ` `  `    ``while` `(temp !``=` `None``): ` `     `  `        ``if` `(temp.data > first) : ` `            ``second ``=` `first  ` `            ``first ``=` `temp.data  ` `         `  `        ``# If current node's data is in between  ` `        ``# first and second then update second  ` `        ``elif` `(temp.data > second ``and` `temp.data !``=` `first) : ` `            ``second ``=` `temp.data  ` ` `  `        ``temp ``=` `temp.``next` ` `  `    ``if` `(second ``=``=` `-``323767``) : ` `        ``print``( ``"There is no second largest element\n"``)  ` `    ``else``: ` `        ``print` `(``"The second largest element is "` `, second)  ` ` `  `# Driver code ` ` `  `start ``=` `None` ` `  `# The constructed linked list is:  ` `# 12 . 35 . 1 . 10 . 34 . 1  ` `start ``=` `push(start, ``1``)  ` `start ``=` `push(start, ``34``)  ` `start ``=` `push(start, ``10``)  ` `start ``=` `push(start, ``1``)  ` `start ``=` `push(start, ``35``)  ` `start ``=` `push(start, ``12``)  ` ` `  `print2largest(start)  ` ` `  `# This code is contributed by Arnab Kundu `

## C#

 `// C# program to print second largest  ` `// value in a linked list  ` `using` `System; ` ` `  `class` `GFG ` `{ ` `     `  `// A linked list node  ` `public` `class` `Node  ` `{  ` `    ``public` `int` `data;  ` `    ``public` `Node next;  ` `};  ` ` `  `// Function to add a node at the  ` `// beginning of Linked List  ` `static` `Node push( Node head_ref, ``int` `new_data)  ` `{  ` `    ``// allocate node  ` `    ``Node new_node = ``new` `Node();  ` ` `  `    ``// put in the data  ` `    ``new_node.data = new_data;  ` ` `  `    ``// link the old list off the new node  ` `    ``new_node.next = (head_ref);  ` ` `  `    ``// move the head to point to the new node  ` `    ``(head_ref) = new_node;  ` `    ``return` `head_ref; ` `}  ` ` `  `// Function to count size of list  ` `static` `int` `listSize( Node node)  ` `{  ` `    ``int` `count = 0;  ` ` `  `    ``while` `(node != ``null``) ` `    ``{  ` `        ``count++;  ` ` `  `        ``node = node.next;  ` `    ``}  ` ` `  `    ``return` `count;  ` `}  ` ` `  `// Function to print the second  ` `// largest element  ` `static` `void` `print2largest(Node head)  ` `{  ` `    ``int` `first, second;  ` ` `  `    ``int` `list_size = listSize(head);  ` ` `  `    ``// There should be atleast two elements ` `    ``if` `(list_size < 2)  ` `    ``{  ` `        ``Console.Write(``"Invalid Input"``);  ` `        ``return``;  ` `    ``}  ` ` `  `    ``first = second = ``int``.MinValue;  ` ` `  `    ``Node temp = head;  ` ` `  `    ``while` `(temp != ``null``) ` `    ``{  ` `        ``if` `(temp.data > first)  ` `        ``{  ` `            ``second = first;  ` `            ``first = temp.data;  ` `        ``}  ` ` `  `        ``// If current node's data is in between  ` `        ``// first and second then update second  ` `        ``else` `if` `(temp.data > second &&  ` `                 ``temp.data != first)  ` `            ``second = temp.data;  ` ` `  `        ``temp = temp.next;  ` `    ``}  ` ` `  `    ``if` `(second == ``int``.MinValue)  ` `        ``Console.Write( ``"There is no second"` `+ ` `                       ``" largest element\n"``);  ` `    ``else` `        ``Console.Write(``"The second largest "` `+  ` `                      ``"element is "` `+ second);  ` `}  ` ` `  `// Driver Code ` `public` `static` `void` `Main(String []args) ` `{  ` `    ``Node start = ``null``;  ` ` `  `    ``// The constructed linked list is:  ` `    ``//12 . 35 . 1 . 10 . 34 . 1  ` `    ``start = push(start, 1);  ` `    ``start = push(start, 34);  ` `    ``start = push(start, 10);  ` `    ``start = push(start, 1);  ` `    ``start = push(start, 35);  ` `    ``start = push(start, 12);  ` ` `  `    ``print2largest(start);  ` `} ` `}  ` ` `  `// This code is contributed by 29AjayKumar `

Output:

```The second largest element is 34
```

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