下面这段代码试了一下，可以优化 20% 左右。

#include <vector>
#include <cmath>
#include <iostream>

using namespace std;

int intperf()
{
    constexpr int n = 5000 * 10000;
    bool found = false;
    vector<int> primes;
    primes.reserve(n);
    primes.push_back(2);
    primes.push_back(2);
    primes.push_back(2);
    primes.push_back(2);
    for (int i = 3; i <= n; i += 2) {
        int t = static_cast<int>(primes.size()) - 4;
        for (int it = 0; it <= t ; it += 4) {
            int j0 = primes[it + 0];
            int j1 = primes[it + 1];
            int j2 = primes[it + 2];
            int j3 = primes[it + 3];
            if ((i % j0 == 0) || (i % j1 == 0) || (i % j2 == 0) || (i % j3 == 0)) {
                found = true;
                break;
            }
            if (j0 * j0 > i) {
                break;
            }
        }
        if (!found) {
            primes[t + 1] = i;
            primes.push_back(2);
        } else {
            found = false;
        }
    }
    return primes.size() - 3;
}

int main()
{
    cout << intperf() << endl;
    return 0;
}

【 在 hgoldfish (老鱼) 的大作中提到: 】
: 随便写的代码，cpp 还经常弱于 python 和 c# 呢。c# 和 python 底层用的都是优化过的 c 代码。
: 我觉得 cpp 写代码的好处在于优化上限高，内存占用低。我优化一下这段代码看看。。
--
修改:hgoldfish FROM 124.72.118.*
FROM 124.72.118.*