Prime visits - what is the error?

#1

import java.util.*;
public class Main {
public static void main(String args[]) {

	Scanner scn = new Scanner(System.in);
	int n = scn.nextInt();
	for(int i= 0; i <n ;i++){
		int a =  scn.nextInt();
		int b = scn.nextInt();
	
	System.out.println(primevisit(a,b));
	}
}
	
public static int primevisit(int a,int b){

	int c = 1;
	int flag =1;
	for(int i = a; i<=b ;i++) {
		
	for(int div = 2 ; div < i ; div++){
		if( i % div == 0){
			flag = 0;
			break;
		}
	}

	if ( flag == 1) {
		c = c+1;
	}
	}
	return c;
}

}

#2

@asthaaggarwal2,

You are supposed to use the prime seive optimisation technique. Also make sure that you call the primeseive function that you will make before the test cases only to prevent TLE.

Precompute the prime numbers using sieve technique.

In the sieve technique where you create a boolean array of 1000005 size.

And start from the first prime number i.e. 2. Take its square(4) and increment it by the number you took (i.e. 4,6,8,10 and so on). Mark all these as false since they cannot be primes.

Now take the next unmarked number, 3. And mark 9,12,15 and so as false. Similarly do it for 4. 16,20,24 and so on as false.

When you finish the loop, count the number of primes within the range.

#3

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