LeetCode OJ：Count Primes（质数计数）

 1 class Solution {
 2 public:
 3     int countPrimes(int n) {
 4         vector<int> vtor(n + 1, 0);
 5         vector<int> ret;
 6         for (int i = 0; i <= n; ++i)
 7             vtor[i] = i;
 8         for (int i = 2; i < n; ++i){//边界条件注意
 9             if (vtor[i] != -1){
10                 ret.push_back(vtor[i]);
11                 int tmpPrime = vtor[i];
12                 for (int mul = 1; tmpPrime * mul <= n; mul++){
13                     vtor[tmpPrime * mul] = -1;
14                 }
15             }
16         }
17         return ret.size();
18     }
19 };