백준 소스코드 [C++] 4948 베르트랑 공준

https://www.acmicpc.net/problem/4948

4948번: 베르트랑 공준

백준 소스코드 [C++] 4948 베르트랑 공준

#include <iostream>
#include <algorithm>
#include <cmath>
using namespace std;
int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	int b = 123456*2;
	bool* arr = new bool[b+1];
	for (int i = 2;i <= b;i++) arr[i] = true;
	for (int i = 2;i <= sqrt(b);i++)
		if (arr[i])
			for (int j = i + i;j <= b;j = j + i)arr[j] = false;
	int n;
	while (true) {
		cin >> n;
		if (n == 0) break;
		int stack = 0;
		for (int i = n+1;i <= 2 * n;i++) if (arr[i] == true) stack++;
		cout << stack << '\n';
	}
	return 0;
}