Java Prime Prime Numbers-leetcode 204

Description:

Count the number of prime numbers less than a non-negative number, n

Click to show more hints.

Credits:
Special thanks to @mithmatt for adding this problem and creating all test cases.

For all primes within N, previously seen a topic, by marking out all non-primes, and then finding the prime number, the code is as follows:

1      Public intCountPrimes (intN) {2         if(n = = 0 | | n = = 1 | | n = = 2)3             return0;4         int[] flag =New int[n];5          for(inti = 2; I < math.sqrt (flag.length); i++) {6             if(Flag[i] = = 0)7                  for(intj = i; I * J < flag.length; J + +) {8Flag[i * j] = 1;9                 }Ten         } One         intCount = 0; A          for(inti = 2; i < flag.length; i++) -Count + =Flag[i]; -BitSet bs =NewBitSet (); the bs.ne -         returnFlag.length-count-2; -}

It is worth noting that the outer loop only needs to be to the square root of N, because the inner loop begins with the i*j. In Leetcode, if no Gargan, it will overflow.

Java Prime Prime Numbers-leetcode 204