Write a function that counts the number of primes in the
range [1-N]. Write the test cases for this function.
Answers were Sorted based on User's Feedback
Answer / himanshu
Well this is what I tried to make it more simple, no list...
just checking and calling functions.
int calculate_prime(int prime_no)
{
int check,count=0;
while(prime_no != 0)
{
check=check_prime(prime_no);
if (check == 0)
count++;
prime_no--;
}
return count;
}
int check_prime(int prime_no)
{
int num,prime_check=0;
num=prime_no/2;
while(num > 1)
{
if( (prime_no%num) == 0 )
{
prime_check=1;
break;
}
num--;
}
return prime_check;
}
void main()
{
int a;
//TEST CASE 1:
//PASSING 11 AS ARGUEMENT TO calculate_prime FUNCTION
//PREFERRED OUTPUT SHOULD BE 6
a=calculate_prime(11);
printf("%d",a);
//TEST CASE 2:
//PASSING 10 AS ARGUEMENT TO calculate_prime FUNCTION
//PREFERRED OUTPUT SHOULD BE 5
a=calculate_prime(10);
printf(" , %d",a);
getch();
}
Is This Answer Correct ? | 2 Yes | 3 No |
Answer / softwareguy
This is what I came up with (C#):
PSEUDO:
-Craete a list of numbers uptill n number - n being int
parameter
-Pass this list into a function to check for primilaty for
the number and then print primes wile we count for primes
BACKGROUND OF THIS SOLUTION:
THEORY:
- we know primes are the numbers starting from 2 are
divisible with 1 and themselves only i.e. n being a prime
number can only be divisble as n/n or n/1. testing from a
prime is called "primilatiy test" for a number...
-the simplest primality test is to see if given a number n
is divisible by an integer m from 2 to n-1. If n is
divisible by n then n is a composite number otherwise its a
prime...
TO SPEED UP THE COMPUTING WE CAN ALSO:
Rather than testing till n-1 we can test the number till
Square Root of n i.e. if n is a prime number it can always
be factored into 2 values.
REFERENCE:
See here if you want to be a mathematician ;-).
http://en.wikipedia.org/wiki/Primality_test
THE CODE:
I would assume you know how to deal with lists in c# so I
will not get into that. Just create an integer based items
list "list<int>" etc. in C# which adds digits to the list
till number n. HINT: use a for loop ...LOL!!
public void CountPrimes(list<int> c)
{
list<int> primes = c.FindAll(
delegate(int a)
for (int i = 2; i <= Math.Sqrt(a); i++)
{
if (a % i == 0)
return false; //is not a prime
return true;//is a prime
}
//list primes in a list box and get the total count
label1.Text = "Total Primes = " + Convert.ToString
(p.count);
for (int count = 2; count < p.count; count++)
{
listbox.Items.Add(Convert.ToString(p[i]));
}
}
and you are done!!! let me know if this is good enough...
Is This Answer Correct ? | 1 Yes | 4 No |
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