Eddy’s research II

找规律

#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;

typedef long long LL;

int m, n;

LL solve(int m, int n) {
    if (m == 1)
        return n + 2;

    if (m == 2)
        return 2 * n + 3;

    if (m == 3 && n == 0)
        return 5;

    if (m == 3 && n)
        return 2 * solve(3, n - 1) + 3;
}

int main() {
    while (cin >> m >> n) {
        cout << solve(m, n) << endl;
    }

    return 0;
}

找新朋友

#include <iostream>
#include <cstring>
#include <algorithm>
#include <cmath>

using namespace std;

const int N = 32780;

bool st[N];

int main() {
    int t;
    cin >> t;

    while (t -- ) {
        int n;
        cin >> n;

        int ans = n - 1;
        memset(st, false, sizeof st);

        for (int i = 2; i < n; i ++ )

            if (n % i == 0)
                for (int j = i; j < n; j += i)

                    st[j] = true;

        for (int i = 1; i <= n; i ++ )

            if (st[i])
                ans -- ;
        cout << ans << endl;
    }

    return 0;
}

Eddy’s research I

埃式筛法

#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;

const int N = 100010;

int primes[N];
int cnt;
bool st[N];
int a[N];

void get_primes() {
    for (int i = 2; i < N; i ++ ) {

        if (st[i])
            continue;
        primes[cnt ++ ] = i;

        for (int j = i + i; j < N; j += i)

            st[j] = true;
    }
}

int main() {
    get_primes();

    int n;

    while (cin >> n) {
        int j = 0;

        for (int i = 0; i < cnt;) {

            if (n == primes[i]) {
                a[j] = primes[i];
                break;
            } else {
                if (n % primes[i] == 0) {
                    n /= primes[i];
                    a[j ++ ] = primes[i];
                } else
                    i ++ ;
            }
        }

        if (j == 0)
            printf("%d\n", a[j]);
        else {
            for (int i = 0; i < j; i ++ )

                printf("%d*", a[i]);
            printf("%d\n", a[j]);
        }
    }

    return 0;
}

线性筛法

#include <iostream>
#include <cstring>
#include <algorithm>
#include <cmath>

using namespace std;

const int N = 65550;
const int M = 100010;

int primes[N], cnt;
bool st[N];
int a[M];

void get_primes() {
    for (int i = 2; i < N; i ++ ) {

        if (!st[i])
            primes[cnt ++ ] = i;

        for (int j = 0; primes[j] <= N / i; j ++ ) {

            st[primes[j] * i] = true;

            if (i % primes[j] == 0)
                break;
        }
    }
}

int main() {
    get_primes();

    int x;

    while (cin >> x) {
        int j = 0;

        for (int i = 0; i < cnt;) {

            if (x == primes[i]) {
                a[j] = x;
                break;
            }

            if (x % primes[i] == 0) {
                a[j ++ ] = primes[i];
                x /= primes[i];
            } else
                i ++ ;
        }

        if (j == 0)
            printf("%d\n", x);
        else {
            for (int i = 0; i < j; i ++)

                printf("%d*", a[i]);
            printf("%d\n", a[j]);
        }
    }

    return 0;
}

七夕节

#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;

const int N = 500010;

int a[N] = {1};

void init() {
    for (int i = 1; i <= N / 2; i ++ )

        for (int j = i + i; j <= N; j += i)

            a[j] += i;
}

int main() {
    int t;
    cin >> t;

    init();

    while (t -- ) {
        int n;
        cin >> n;

        cout << a[n] << endl;
    }

    return 0;
}