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# Queue Operations

• Last Updated : 29 Sep, 2021

Given N integers, the task is to insert those elements in the queue. Also, given M integers, the task is to find the frequency of each number in the Queue.

Examples:

Input:
N = 8
1 2 3 4 5 2 3 1  (N integers)
M = 5
1 3 2 9 10  (M integers)
Output:
2 2 2 -1 -1

Explanation:
After inserting 1, 2, 3, 4, 5, 2, 3, 1 into the queue,  frequency of 1 is 2, 3 is 2, 2 is 2, 9 is -1 and 10 is -1 (since, 9 and 10 is not there in the queue).

Input:
N = 5
5 2 2 4 5   (N integers)
M = 5
2 3 4 5 1   (M integers)
Output:
2 -1 1 2 -1

Approach: The given problem can be solved by using a simple queue. The idea is to insert N integers one by one into the queue and then check the frequency of M integers. Separate functions will be created to perform both operations. Follow the steps below to solve the problem.

• Create a queue and push all given integers into the queue.
• After pushing all the elements into the queue create another function for counting the frequency of given M elements one by one.
• Take a variable cntFrequency to keep track of frequency of current element.
• Pop all the elements from queue till its size and each time check if current element in queue is equal to element for which we are checking for frequency.
– if both are equal, increment cntFrequency by 1
– else, do nothing.
• Push the current element back to the queue so that for next case queue will not get disturbed.
• Print the frequency of each element found.

Below is the implementation of the above approach:

## Java

 `// Java Program to implement above approach``import` `java.io.*;``import` `java.util.*;` `class` `GFG {` `    ``// Driver code``    ``public` `static` `void` `main(String[] args)``    ``{``        ``// Declaring Queue``        ``Queue q = ``new` `LinkedList<>();``        ``int` `N = ``8``;``        ``int``[] a = ``new` `int``[] { ``1``, ``2``, ``3``, ``4``, ``5``, ``2``, ``3``, ``1` `};``        ``int` `M = ``5``;``        ``int``[] b = ``new` `int``[] { ``1``, ``3``, ``2``, ``9``, ``10` `};` `        ``// Invoking object of Geeks class``        ``Geeks obj = ``new` `Geeks();` `        ``for` `(``int` `i = ``0``; i < N; i++) {``            ``// calling insert()``            ``// to add elements in queue``            ``obj.insert(q, a[i]);``        ``}` `        ``for` `(``int` `i = ``0``; i < M; i++) {``            ``// calling findFrequency()``            ``int` `f = obj.findFrequency(q, b[i]);``            ``if` `(f != ``0``) {``                ``// variable f``                ``// will have final frequency``                ``System.out.print(f + ``" "``);``            ``}``            ``else` `{``                ``System.out.print(``"-1"``                                 ``+ ``" "``);``            ``}``        ``}``    ``}``}` `// Helper class Geeks to implement``// insert() and findFrequency()``class` `Geeks {` `    ``// Function to insert``    ``// element into the queue``    ``static` `void` `insert(Queue q, ``int` `k)``    ``{``        ``// adding N integers into the Queue``        ``q.add(k);``    ``}` `    ``// Function to find frequency of an element``    ``// return the frequency of k``    ``static` `int` `findFrequency(Queue q, ``int` `k)``    ``{``        ``// to count frequency of elements``        ``int` `cntFrequency = ``0``;` `        ``// storing size of queue in a variable``        ``int` `size = q.size();` `        ``// running loop untill size becomes zero``        ``while` `(size-- != ``0``) {` `            ``// storing and deleting``            ``// first element from queue``            ``int` `x = q.poll();` `            ``// comparing if it's equal to integer K``            ``// that belongs to M``            ``if` `(x == k) {``                ``// increament count``                ``cntFrequency++;``            ``}``            ``// add element back to queue because``            ``// we also want N integers``            ``q.add(x);``        ``}``        ``// return the count``        ``return` `cntFrequency;``    ``}``}`

## Python3

 `# Python Program to implement above approach``import` `collections` `# Helper class Geeks to implement``# insert() and findFrequency()``class` `Geeks:` `    ``# Function to insert``    ``# element into the queue``    ``def` `insert(``self``, q, k):``      ` `        ``# adding N integers into the Queue``        ``q.append(k)` `    ``# Function to find frequency of an element``    ``# return the frequency of k``    ``def` `findFrequency(``self``, q, k):``      ` `        ``# to count frequency of elements``        ``cntFrequency ``=` `0` `        ``# storing size of queue in a variable``        ``size ``=` `len``(q)` `        ``# running loop untill size becomes zero``        ``while` `(size):``            ``size ``=` `size ``-` `1``            ` `            ``# storing and deleting``            ``# first element from queue``            ``x ``=` `q.popleft()` `            ``# comparing if it's equal to integer K``            ``# that belongs to M``            ``if` `(x ``=``=` `k):``              ` `                ``# increament count``                ``cntFrequency ``+``=` `1``                ` `            ``# add element back to queue because``            ``# we also want N integers``            ``q.append(x)` `        ``# return the count``        ``return` `cntFrequency` `# Declaring Queue``q ``=` `collections.deque()``N ``=` `8``a ``=` `[``1``, ``2``, ``3``, ``4``, ``5``, ``2``, ``3``, ``1``]``M ``=` `5``b ``=` `[``1``, ``3``, ``2``, ``9``, ``10``]` `# Invoking object of Geeks class``obj ``=` `Geeks()` `for` `i ``in` `range``(N):` `    ``# calling insert()``    ``# to add elements in queue``    ``obj.insert(q, a[i])` `for` `i ``in` `range``(M):` `    ``# calling findFrequency()``    ``f ``=` `obj.findFrequency(q, b[i])``    ``if` `(f !``=` `0``):``      ` `        ``# variable f``        ``# will have final frequency``        ``print``(f, end``=``" "``)``    ``else``:``        ``print``(``"-1"``, end``=``" "``)``print``(``" "``)` `# This code is contributed by gfgking.`

## C#

 `// C# Program to implement above approach``using` `System;``using` `System.Collections.Generic;` `public` `class` `GFG {``  ` `  ``// Helper class Geeks to implement``// insert() and findFrequency()``public` `class` `Geeks {` `    ``// Function to insert``    ``// element into the queue``   ``public` `void` `insert(Queue<``int``> q, ``int` `k)``    ``{``        ``// adding N integers into the Queue``        ``q.Enqueue(k);``    ``}` `    ``// Function to find frequency of an element``    ``// return the frequency of k``    ``public` `int` `findFrequency(Queue<``int``> q, ``int` `k)``    ``{``        ``// to count frequency of elements``        ``int` `cntFrequency = 0;` `        ``// storing size of queue in a variable``        ``int` `size = q.Count;` `        ``// running loop untill size becomes zero``        ``while` `(size-- != 0) {` `            ``// storing and deleting``            ``// first element from queue``            ``int` `x = q.Peek();``            ``q.Dequeue();` `            ``// comparing if it's equal to integer K``            ``// that belongs to M``            ``if` `(x == k) {``                ``// increament count``                ``cntFrequency++;``            ``}``            ``// add element back to queue because``            ``// we also want N integers``            ``q.Enqueue(x);``        ``}``        ``// return the count``        ``return` `cntFrequency;``    ``}``}` `    ``// Driver code``    ``public` `static` `void` `Main()``    ``{``      ` `        ``// Declaring Queue``        ``Queue<``int``> q = ``new` `Queue<``int``>();``        ``int` `N = 8;``        ``int``[] a = ``new` `int``[] { 1, 2, 3, 4, 5, 2, 3, 1 };``        ``int` `M = 5;``        ``int``[] b = ``new` `int``[] { 1, 3, 2, 9, 10 };` `        ``// Invoking object of Geeks class``        ``Geeks obj = ``new` `Geeks();` `        ``for` `(``int` `i = 0; i < N; i++)``        ``{``          ` `            ``// calling insert()``            ``// to add elements in queue``            ``obj.insert(q, a[i]);``        ``}` `        ``for` `(``int` `i = 0; i < M; i++)``        ``{``          ` `            ``// calling findFrequency()``            ``int` `f = obj.findFrequency(q, b[i]);``            ``if` `(f != 0)``            ``{``              ` `                ``// variable f``                ``// will have final frequency``                ``Console.Write(f + ``" "``);``            ``}``            ``else` `{``                ``Console.Write(``"-1"``                                 ``+ ``" "``);``            ``}``        ``}``    ``}``}` `// This code is contributed by SURENDRA_GANGWAR.`
Output
`2 2 2 -1 -1 `

Time Complexity: O(N*M)
Auxiliary Space: O(N)

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