Leetcode----204. Count Primes (Java)

1  PackagecountPrimes204;2 /*3 * Description:4 * Count The number of prime numbers less than a non-negative number, N.5  */6  Public classSolution {7     //Time Limit exceeded8     /*9 public static int countprimes (int n) {Ten int number=0; One for (int i=0;i<n;i++) A if (IsPrime (i) ==true) - number++; - return number; the     } - Public Static Boolean isprime (int n) { - if (n <= 3) - return n > 1; + else if (n%2==0| | n%3==0) - return false; + else{ A for (int i=2;i<=math.sqrt (n); i++) { at if (n%i = = 0) - return false; -                } -            } - return true; -        } in       */ -      to      Public Static intCountPrimes (intN) { +         //Boolean default is False -         Boolean[] Isprime=New Boolean[n]; the         intNumprime=0; *          for(inti=2;i<n;i++){ $             if(isprime[i-1]==false){Panax Notoginsengnumprime++; -                  for(intj=2;i*j<n;j++) theisprime[i*j-1]=true; +             } A         } the         returnNumprime; +     } -      Public Static voidMain (string[] args) { $         //TODO auto-generated Method Stub $System.out.println (CountPrimes (15000000)); -         Boolean[] Isprime=New Boolean[2]; -System.out.println (isprime[0]); the     } -     //ReferenceWuyi      Public intCountPrimes2 (intN) { the         Boolean[] Notprime =New Boolean[n]; -         intCount = 0; Wu          for(inti = 2; I < n; i++) { -             if(Notprime[i] = =false) { Aboutcount++; $                  for(intj = 2; I*j < n; J + +) { -NOTPRIME[I*J] =true; -                 } -             } A         } +         returncount; the     } -}

Leetcode----204. Count Primes (Java)