Unable to compute one test case as TLE

#1

public class Main {
public static void main(String args[]) {
Scanner sc= new Scanner(System.in);
int n= sc.nextInt();
int a[]= new int[n];
for(int i=0;i<n;i++){

	 a[i]= sc.nextInt();
	 
	}
	for(int i=0;i<n;i++){

		int np=1;
		int k=2;
		
		while(np<=a[i]){
			
			boolean isPrime=true;
			
			for(int j=2;(j*j)<=k;j++){
				
				
				 if(k%j==0) {
				isPrime=false;
				   break;
				   }
			}
			
			if(isPrime) 
				np++;
			k++;
		
			
		}
		System.out.println(k-1);
	}
}

}
plz suggest me how can I optimize my code for all the test cases

#2

@Vishu_1801,
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 b+1 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 all the positions marked as true and when count is equal to the given test case value print that index. This will be our final answer.

#3

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