UVa 10539 - Almost Prime Numbers

通过这题学习了线性筛法素数打表的方法，题目本身更像数学思考题。

#include <iostream>
#include <cstdio>
#include <cmath>
#include <vector>
#include <cstring>
using namespace std;
using LL = long long int;

const int maxn = 1024000;
bool check[maxn];
LL pri[maxn], tot;

void init()
{
	for (int i = 2; i < maxn; ++i){
		if (!check[i]) pri[tot++] = i;
		for (int j = 0; j < tot; ++j){
			if (pri[j] * i > maxn) break;
			check[pri[j]*i] = true;
			if (i % pri[j] == 0) break;
		}
	}
}
int main()
{
	init(); int T; cin >> T;
	while (T--){
		LL L, U, res = 0; cin >> L >> U;
		for (int i = 0; i < tot && pri[i] * pri[i] <= U; ++i){
			LL cur = pri[i] * pri[i];
			while (cur <= U){
				if (cur >= L) ++res;
				cur *= pri[i];
			}
		}
		cout << res << endl;
	}
	return 0;
}