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  1. import java.io.*;
  2. import java.util.*;
  3. class Simple //print prime numbers <=N. O(N loglogN). Eratosthenes
  4. {
  5.     public static void main(String args[]) throws IOException
  6.     {
  7.         BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
  8.  
  9.         int N;
  10.         long i,j;
  11.  
  12.         System.out.println("Enter N");
  13.         N=Integer.parseInt(br.readLine().trim());
  14.  
  15.         long start=System.nanoTime();
  16.         boolean a[]=new boolean [N+1];
  17.         Arrays.fill(a,true);
  18.  
  19.         a[0]=false;
  20.         a[1]=false;
  21.  
  22.         for(i=2;i<=N;i++)
  23.         {
  24.             if(a[(int)i]==true)
  25.             {
  26.                 for(j=i*i;j<=N;j+=i)
  27.                 a[(int)j]=false;
  28.             }
  29.         }
  30.  
  31.         long end=System.nanoTime();
  32.         double ans=((double)(end-start))/1000000000;
  33.         System.out.println("\nTime in seconds:");
  34.         System.out.println(ans+"\n");
  35.         System.out.println("Primes less than N :");
  36.         //for(i=2;i<=N;i++)
  37.         //{
  38.         //    if(a[(int)i]==true)
  39.         //    System.out.print(i+" ");
  40.        // }
  41.     }
  42. }
Success #stdin #stdout 0.12s 38156KB
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stdin
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10000000
stdout
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Enter N

Time in seconds:
0.068977386

Primes less than N :
https://ideone.com/mhIdUs
language:
Java (HotSpot 12)
created:
5 years ago
visibility:
secret

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