To find count of prime between a range

#1

package learn_java;
import java.util.;
class A_class{
public static void main(String args[]) {
Scanner sc=new Scanner(System.in);
int t=sc.nextInt();
int c=1000000;
int a[]=new int [1000005];
int p[]=prime_sieve(a,c);
while(t–>0) {
int s=sc.nextInt();
int e=sc.nextInt();
System.out.println(p[e]-p[s-1]);
}
}
static int[] prime_sieve(int a[],int c) {
for(int i=3;i<c;i=i+2 ) {
a[i]=1;
}
for(int i=3;i<c;i++) {
if(a[i]==1) {
for(int j=ii;j<c;j=j+i) {
a[j]=0;
}
}
}
a[0]=a[1]=0;
a[2]=1;
int p[]=new int[c+5];
for(int i=0;i<c;i++) {
if(i>0) {
p[i]=a[i]+a[i-1];

		}else {
			p[i]=a[i];
		}
	}
	return p;
}

}

#2

Can you pls tell the logic you have used… since I m not able to get your solution…as wht approach you have used.

#3

1- I created an array and marked all odd position as 1.
2-then i run a loop and marked all position which is at multiple of 3 ,…then multiple of 5 …then 7.
3-then i created an array and store count of prime till any number ex-20,30,70.

#4

Use the following logic in your code as,

void primeseive(long long int p[1000000],long long int N)
{
p[0]=p[1]=0;
p[2]=1;
for(long long int i=3;i<N;i=i+2)
{
p[i]=1;
}
for(long long int i=3;i<N;i=i+2)
{
if(p[i])
{
for(long long int j=ii;j<N;j=j+2i)
{
p[j]=0;
}
}
}
return;
}

and in the main you can maintain as :

long long int N=1000000;
long long int p[N];
primeseive(p,N);

for(long long int i=a;i<=b;i++)
{
if(p[i]==1)
{
cnt=cnt+1;
}
}
cout<<cnt<<endl;

This is the basic approach you can follow in your code…

#5

Hey @Affan-Mokarram-202031887744398
How can I help you ?

#6

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