leetcode--Count Primes

Description:

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

[java] view plain copy

1. public class Solution {  
2.     public int countPrimes(int n) {  
3.         if(n<2) return 0;  
4.         boolean[] flag = new boolean[n+1];  
5.         int count = 0;  
6.         for(int i=2;i<n;i++){  
7.             if(!flag[i]){//如果是质数，则将其倍数设置为非质数  
8.                 for(int j=2;i*j<=n;j++){  
9.                     flag[i*j] = true;  
10.                 }  
11.             }  
12.         }  
13.         for(int i=2;i<n;i++){  
14.             if(!flag[i]) count++;  
15.         }  
16.         return count;  
17.     }  
18. }  

原文链接http://blog.csdn.net/crazy__chen/article/details/45440035