How do I calculate the sum of the multiplications of combinations?

Question

1.00/5 (1 vote)

See more:

I wrote a code to calculate this series but the output is not correct.
Please tell me what the problem is؟
I think the problem is with the Calc function but I can not solve it

Calc(n)=
 
n   i
∑   ∏ c(i,j)
i=1 j=1

input = 3
output = 12

What I have tried:

import java.util.*;
public class Main
{
	public static void main(String[] args) {
	   Scanner input = new Scanner(System.in);
	   
	   int n = input.nextInt();
	   Calc(n);
	    
	   
	}
////////////////////////////////////////////////////	
	public static int fact(int n) {
	    
    int fact = 1;
    for (int i = 2; i <= n; i++) {
        fact = fact * i;
    } 
   
    return fact;

}
//////////////////////////////////////////////////////
public static int Comb(int n,int m){
    
     int c = (int)(fact(n) 
                      / (fact(n - m) * fact(m)));
                      
       return c;  
   
}
//////////////////////////////////////////////////////
public static void Calc(int n){
    int combi = 1;
    int sum   = 0;
   
    for(int i=1,j=1; i <= n; i++ ){
      
        for(int j=1; j <= i ; j++){ 
            
            combi*=Comb(i,j);
               
           
        } sum+=combi;
          System.out.println(sum);
       
    }
    
  
    
}


}

Posted 2-Dec-21 22:33pm

urmiye city

Updated 3-Dec-21 2:08am

v3

Add a Solution

Comments

phil.o 3-Dec-21 4:39am

Please indicate which number your are using as input.

Richard MacCutchan 3-Dec-21 4:49am

Which function? What are the inputs? What result do you expect, and what do you actually see?

Richard MacCutchan 3-Dec-21 5:00am

When I enter the value 3 I get 21 as the result.

2 solutions

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

OriginalGriff · Answer 1 · 2021-12-02T23:05:00

Compiling does not mean your code is right! :laugh:
Think of the development process as writing an email: compiling successfully means that you wrote the email in the right language - English, rather than German for example - not that the email contained the message you wanted to send.

So now you enter the second stage of development (in reality it's the fourth or fifth, but you'll come to the earlier stages later): Testing and Debugging.

Start by looking at what it does do, and how that differs from what you wanted. This is important, because it give you information as to why it's doing it. For example, if a program is intended to let the user enter a number and it doubles it and prints the answer, then if the input / output was like this:

Input   Expected output    Actual output
  1            2                 1
  2            4                 4
  3            6                 9
  4            8                16

Then it's fairly obvious that the problem is with the bit which doubles it - it's not adding itself to itself, or multiplying it by 2, it's multiplying it by itself and returning the square of the input.
So with that, you can look at the code and it's obvious that it's somewhere here:

int Double(int value)
   {
   return value * value;
   }

Once you have an idea what might be going wrong, start using the debugger to find out why. Put a breakpoint on the first line of the method, and run your app. When it reaches the breakpoint, the debugger will stop, and hand control over to you. You can now run your code line-by-line (called "single stepping") and look at (or even change) variable contents as necessary (heck, you can even change the code and try again if you need to).
Think about what each line in the code should do before you execute it, and compare that to what it actually did when you use the "Step over" button to execute each line in turn. Did it do what you expect? If so, move on to the next line.
If not, why not? How does it differ?
Hopefully, that should help you locate which part of that code has a problem, and what the problem is.
This is a skill, and it's one which is well worth developing as it helps you in the real world as well as in development. And like all skills, it only improves by use!

CPallini · Answer 2 · 2021-12-03T02:08:00

There are some problems in your code.
Try (not properly checked).
Beware: factorial explodes very fast!

Java

import java.util.*;
public class Main
{
  public static void main(String[] args)
  {
     Scanner input = new Scanner(System.in);

     int n = input.nextInt();
     System.out.println(Calc(n));
  }

  ////////////////////////////////////////////////////  

  // 'low bounded' factorial, computes:  n*(n-1)*...(m+1)
  public static int lbfact(int n, int m)
  {

    int upper_fact = 1;
    while ( n > m)
    {
      upper_fact *= n;
      --n;
    }
    return upper_fact;
  }

  public static int fact(int n)
  {
    return lbfact(n,0);
  }


  //////////////////////////////////////////////////////
  public static int Comb(int n, int m)
  {
    if ( m < n/2 )
      m = (n-m);

    return ( lbfact(n,m) / fact(n-m));
  }

  //////////////////////////////////////////////////////
  public static int Calc(int n)
  {
    int sum   = 0;

    for(int i=1; i <= n; i++ )
    {
      int combi = 1;
      for(int j=1; j <= i ; j++)
      {
        combi *= Comb(i,j);
      }
      sum += combi;

    }
    return sum;
  }
}

How do I calculate the sum of the multiplications of combinations?

2 solutions

Solution 1

Solution 2

Add your solution here

Preview 0