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Probability of finding an element K in a Singly Linked List
• Last Updated : 18 Jun, 2021

Given a Singly Linked List of size N and another key K, we have to find the probability that the key K is present in the Singly Linked List.
Examples:

Input: Linked list = 2 -> 3 -> 3 -> 3 -> 4 -> 2, Key = 5
Output:
Explanation:
Since the value of Key is 5 which is not present in List, the probability of finding the Key in the Linked List is 0.
Input: Linked list = 2 -> 3 -> 5 -> 1 -> 9 -> 8 -> 0 -> 7 -> 6 -> 5, Key = 5
Output: 0.2

Approach:
The probability of finding a Key element K in a Singly Linked List is given below:

Probability = Number of Occurrences of Element K / Size of the Linked List

In our approach, we will first count the number of Element K present in the Singly Linked List and then the probability will be calculated by dividing the number of occurrences of K by the size of the Singly Linked List.
Below is the implementation of the above approach:

## C

 `// C code to find the probability``// of finding an Element``// in a Singly Linked List` `#include ``#include ` `// Link list node``struct` `Node {``    ``int` `data;``    ``struct` `Node* next;``};` `/* Given a reference (pointer to pointer)``   ``to the head of a list and an int,``   ``push a new node on the front of the 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;``}` `// Counts nnumber of nodes in linked list``int` `getCount(``struct` `Node* head)``{` `    ``// Initialize count``    ``int` `count = 0;` `    ``// Initialize current``    ``struct` `Node* current = head;` `    ``while` `(current != NULL) {``        ``count++;``        ``current = current->next;``    ``}``    ``return` `count;``}` `float` `kPresentProbability(``    ``struct` `Node* head,``    ``int` `n, ``int` `k)``{` `    ``// Initialize count``    ``float` `count = 0;` `    ``// Initialize current``    ``struct` `Node* current = head;` `    ``while` `(current != NULL) {``        ``if` `(current->data == k)``            ``count++;``        ``current = current->next;``    ``}``    ``return` `count / n;``}` `// Driver Code``int` `main()``{``    ``// Start with the empty list``    ``struct` `Node* head = NULL;` `    ``// Use push() to construct below list``    ``// 1->2->1->3->1``    ``push(&head, 2);``    ``push(&head, 3);``    ``push(&head, 5);``    ``push(&head, 1);``    ``push(&head, 9);``    ``push(&head, 8);``    ``push(&head, 0);``    ``push(&head, 7);``    ``push(&head, 6);``    ``push(&head, 5);` `    ``printf``(``"%.1f"``,``           ``kPresentProbability(``               ``head, getCount(head), 5));` `    ``return` `0;``}`

## Java

 `// Java code to find the probability``// of finding an Element``// in a Singly Linked List``class` `GFG{` `// Link list node``static` `class` `Node``{``  ``int` `data;``  ``Node next;``};` `// Given a reference (pointer to``// pointer) to the head of a list``// and an int, push a new node``// on the front of the 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;``}` `// Counts nnumber of nodes``// in linked list``static` `int` `getCount(Node head)``{``  ``// Initialize count``  ``int` `count = ``0``;` `  ``// Initialize current``  ``Node current = head;` `  ``while` `(current != ``null``)``  ``{``    ``count++;``    ``current = current.next;``  ``}``  ``return` `count;``}` `static` `float` `kPresentProbability(Node head,``                                 ``int` `n, ``int` `k)``{``  ``// Initialize count``  ``float` `count = ``0``;` `  ``// Initialize current``  ``Node current = head;` `  ``while` `(current != ``null``)``  ``{``    ``if` `(current.data == k)``      ``count++;``    ``current = current.next;``  ``}``  ``return` `count / n;``}` `// Driver Code``public` `static` `void` `main(String[] args)``{``  ``// Start with the empty list``  ``Node head = ``null``;` `  ``// Use push() to conbelow list``  ``// 1.2.1.3.1``  ``head = push(head, ``2``);``  ``head = push(head, ``3``);``  ``head = push(head, ``5``);``  ``head = push(head, ``1``);``  ``head = push(head, ``9``);``  ``head = push(head, ``8``);``  ``head = push(head, ``0``);``  ``head = push(head, ``7``);``  ``head = push(head, ``6``);``  ``head = push(head, ``5``);` `  ``System.out.printf(``"%.1f"``, kPresentProbability(``                     ``head, getCount(head), ``5``));` `}``}` `// This code is contributed by shikhasingrajput`

## Python3

 `# Python3 code to find the probability``# of finding an Element``# in a Singly Linked List` `# Node class``class` `Node:``    ` `    ``def` `__init__(``self``, data, ``next` `=` `None``):``        ` `        ``self``.data ``=` `data``        ``self``.``next` `=` `None` `class` `LinkedList:``    ` `    ``def` `__init__(``self``):``        ` `        ``self``.head ``=` `None``    ` `    ``def` `push(``self``, data):``        ` `        ``# Allocate the Node &``        ``# put the data``        ``new_node ``=` `Node(data)``        ` `        ``# Make the next of new Node as head``        ``new_node.``next` `=` `self``.head``        ` `        ``# Move the head to point to new Node``        ``self``.head ``=` `new_node` `    ``# Counts the number of nodes in linkedlist``    ``def` `getCount(``self``):``        ` `        ``# Initialize current``        ``current ``=` `self``.head``        ` `        ``# Initialize count``        ``count ``=` `0``        ` `        ``while` `current ``is` `not` `None``:``            ``count ``+``=` `1``            ``current ``=` `current.``next``        ` `        ``return` `count``    ` `    ``def` `kPresentProbability(``self``, n, k):``        ` `        ``# Initialize current``        ``current ``=` `self``.head``        ` `        ``# Initialize count``        ``count ``=` `0.0``        ` `        ``while` `current ``is` `not` `None``:``            ``if` `current.data ``=``=` `k:``                ``count ``+``=` `1``                ` `            ``current ``=` `current.``next``        ` `        ``return` `count ``/` `n``    ` `# Driver Code``if` `__name__ ``=``=` `"__main__"``:``    ` `    ``# Start with empty list``    ``llist ``=` `LinkedList()``    ` `    ``# Use push to construct the linked list``    ``llist.push(``2``)``    ``llist.push(``3``)``    ``llist.push(``5``)``    ``llist.push(``1``)``    ``llist.push(``9``)``    ``llist.push(``8``)``    ``llist.push(``0``)``    ``llist.push(``7``)``    ``llist.push(``6``)``    ``llist.push(``5``)``    ` `    ``print``(llist.kPresentProbability(``          ``llist.getCount(), ``5``))``    ` `# This code is contributed by kevalshah5   `

## C#

 `// C# code to find the probability``// of finding an Element``// in a Singly Linked List``using` `System;``class` `GFG{` `// Link list node``class` `Node``{``  ``public` `int` `data;``  ``public` `Node next;``};` `// Given a reference (pointer to``// pointer) to the head of a list``// and an int, push a new node``// on the front of the 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;``}` `// Counts nnumber of nodes``// in linked list``static` `int` `getCount(Node head)``{``  ``// Initialize count``  ``int` `count = 0;` `  ``// Initialize current``  ``Node current = head;` `  ``while` `(current != ``null``)``  ``{``    ``count++;``    ``current = current.next;``  ``}``  ``return` `count;``}` `static` `float` `kPresentProbability(Node head,``                                 ``int` `n, ``int` `k)``{``  ``// Initialize count``  ``float` `count = 0;` `  ``// Initialize current``  ``Node current = head;` `  ``while` `(current != ``null``)``  ``{``    ``if` `(current.data == k)``      ``count++;``    ``current = current.next;``  ``}``  ``return` `count / n;``}` `// Driver Code``public` `static` `void` `Main(String[] args)``{``  ``// Start with the empty list``  ``Node head = ``null``;` `  ``// Use push() to conbelow list``  ``// 1.2.1.3.1``  ``head = push(head, 2);``  ``head = push(head, 3);``  ``head = push(head, 5);``  ``head = push(head, 1);``  ``head = push(head, 9);``  ``head = push(head, 8);``  ``head = push(head, 0);``  ``head = push(head, 7);``  ``head = push(head, 6);``  ``head = push(head, 5);` `  ``Console.Write(``"{0:F1}"``, kPresentProbability(``                 ``head, getCount(head), 5));``}``}` `// This code is contributed by Princi Singh`

## Javascript

 ``
Output
`0.2`

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