题解 | #G题 lower_bound写法#

#include <bits/stdc++.h>

using namespace std;

const int N = 1e7 + 10;

bool st[N];
vector<int> primes;

int n;

void get_prime(int x)
{
    for(int i = 2; i <= x; i++)
    {
        if(!st[i]) primes.push_back(i);
        for(int j = 0; primes[j] <= x / i; j++)
        {
            st[primes[j] * i] = true;
            if(i % primes[j] == 0) break;
        }
    }
}

int main()
{
    cin >> n;
    get_prime(10000010);
    
    while(n--)
    {
        int l, r;
        cin >> l >> r;
**      auto l1 = lower_bound(primes.begin(), primes.end(), l);
        auto l2 = lower_bound(primes.begin(), primes.end(), r);
        
        if(*l2 != r) cout << l2 - l1 << endl;
        else cout << l2 - l1 + 1 << endl;**
    }
    
    return 0;
}