Shirt - Matching Pairs

                      Shirt - Matching Pairs

                                   

A shop to increase sales during a festival has an offer that a customer will get a discount if the customer buys shirts having same size in pairs. Any customer who buys will choose N shirts and the size of the shirt is denoted by S(i) where 1 <= i <=N. Two shirts S(i) and S(j) are matching and form a pair only if S(i) = S(j).

The program must print the number of pairs eligible for the discount.

Input Format:
The first line will contain the value of N
The second line will contain the the size of N shirts S(1) to S(N) with each size separated by a space.

Output Format:
The first line will contain the number of matching pairs eligible for the discount.

Constraints:
2 <= N <= 100

Example Input/Output 1:
Input:
9
10 20 20 10 10 30 44 10 20

Output:
3

Explanation:
The matching pairs are (10,10) (20,20) (10,10).

Example Input/Output 2:
Input:
6
42 44 40 42 44 42

Output:
2

Explanation:
The matching pairs are (42,42) (44,44)

Code:

import java.util.*;

public class Hello {

    public static void main(String[] args) {

                   Scanner sc=new Scanner(System.in);

                   List<Integer> li=new ArrayList<Integer>();

                   Set<Integer> set=new HashSet<Integer>();

                   int i,n=sc.nextInt();

                   int arr[]=new int[n];

                   for(i=0;i<n;i++)

                   {

                       arr[i]=sc.nextInt();

                       li.add(arr[i]);

                       set.add(arr[i]);

                   }

                   int freq,count=0;

                   for(int no:set)

                   {

                       freq=Collections.frequency(li,no);

                       if(freq%2==1)

                           --freq;

                          if(freq%2==0)

                           {

                               freq/=2;

                               count+=freq;

                           }

                   }

                   System.out.print(count);

          }

}

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