Permutations in which n people can occupy r seats in a classroom in java

September 30, 2022

Which n people can occupy r seats in a classroom in Java

Our Aim is to write a Java code to find all the possible permutations in which (n) people can occupy (r) number of seats in a classroom.

Suppose (n) number  students are looking to find (r) seats in a classroom so how will they do it . They will do it with simple formula which is given by 

                                                                n P r  =    n! / (n-r)!

Permutation

Problem Statement :

In a classroom some of the seats are already occupied by students and only a few seats are available in the classroom. The available seats are assumed as r and n number of students are looking for the seat. We need to find in how many different permutations n number of students can sit on r number of chairs.

Algorithm

  • Input number of students in n
  • Input number of seats in r
  • Use permutation formula { factorial(n) / factorial(n-r) }
  • Print Output
Permutations in Java

Octal to Binary conversion

 

Maximum number of handshakes

Addition of two fractions

Replace all 0’s with 1 in a given integer

Java code

Run 
import java.util.*;  
import java.io.*;

public class Main
    {  
      public static void main(String[] args)  
        {  

            int n, r, per, fact1, fact2;  

            Scanner sc =  new Scanner(System.in);  

            System.out.println("Enter the Value of n: ");  
            n = sc.nextInt();

            System.out.println("Enter the Value of r: ");
            r = sc.nextInt();  

            fact1 = 1;  

            for (int i = n; i > 1; i=i-1)  
            {  
                fact1 = fact1 * i;  //calculating factorial (n!)
            }  

            int number;  

            number = n - r;  

            fact2 = 1;  

            for (int i = number; i > 1; i=i-1)  
            {  
                fact2 = fact2 * i;  //calculating factorial ((n-r)!)
            }  

            per = fact1 / fact2;  //calculating  nPr

            System.out.println(per+" ways");  
    }  
}

Output

Enter number of people: 5
Enter number of seats: 9
Total possible arrangements: 120

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5 comments on “Permutations in which n people can occupy r seats in a classroom in java”


  • Mohammed

    import java.util.*;
    public class Permutatuins {
    public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    System.out.println(“n?????????????”);
    int n = sc.nextInt();
    System.out.println(“r?????????????”);
    int r = sc.nextInt();
    int res = fact(n)/(fact(n-r));
    System.out.println(“Total No.of combinations possible: “+res);
    }
    public static int fact(int num) {
    int res =1;
    for(int i=1;i<=num;i++) {
    res=res*i;
    }
    return res;
    }
    }


  • siddeshaob2001

    Permutations are defined for n items taken r at a time, and in your code, you have set r to 9, which is greater than n, which is 5. This is why you’re getting an incorrect result.


      • janhwianand

        import java.util.*;
        public class Permutation {
        public static int fact(int n){
        int f=1;
        for(int i=1;i<=n;i++){
        f=f*i;
        }
        return f;
        }
        public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int n=sc.nextInt();
        int r=sc.nextInt();
        int res=fact(n)/fact(n-r);
        System.out.println(res);
        }
        }


  • Aman

    public static int findFactorial(int number){
    if(number == 0){
    return 1;
    }
    else {
    return number * findFactorial(number – 1);
    }
    }

    public static int PermutionOfNPeopleRSeats(int people_r, int seats_n){

    int denom = seats_n – people_r;
    return (findFactorial(seats_n))/ (findFactorial(denom));
    }

    public static void main(String[] args) {

    int factNumber = PermutionOfNPeopleRSeats(5,9);
    System.out.println(factNumber);
    }