백준 1124번 언더프라임

문제 링크입니다: https://www.acmicpc.net/problem/1124

에라토스테네스의 체를 이용하여 간단히 풀 수 있는 문제였습니다.

#include <iostream>

#include <vector>

using namespace std;

 

const int MAX = 100000 + 1;

 

int minFactor[MAX];

vector<int> prime;

 

void eratosthenes(void)

{

        minFactor[0] = minFactor[1] = -1;

        for (int i = 2; i < MAX; i++)

                 minFactor[i] = i;

 

        for (int i = 2; i*i < MAX; i++)

                 if (minFactor[i] == i)

                         for (int j = i * i; j < MAX; j += i)

                                 if (minFactor[j] == j)

                                          minFactor[j] = i;

 

        for (int i = 2; i < MAX; i++)

                 if (minFactor[i] == i)

                         prime.push_back(i);

}

 

int main(void)

{

        ios_base::sync_with_stdio(0);

        cin.tie(0);

        int A, B;

        cin >> A >> B;

 

        int result = 0;

        eratosthenes();

        for (int i = A; i <= B; i++)

        {

                 int cnt = 0;

                 int temp = i;

                 for (int j = 0; j < prime.size(); j++)

                 {

                         while (!(temp % prime[j]))

                         {

                                 cnt++;

                                 temp /= prime[j];

                                 if (temp == 1)

                                          break;

                         }

                         if (temp == 1)

                                 break;

                 }

                 if (minFactor[cnt] == cnt)

                         result++;

        }

        cout << result << "\n";

        return 0;

}

개발환경:Visual Studio 2017

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