HDU - 2841 Visible Trees （容斥原理）

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
ll prim[100005], lenp = 0, isprim[100005] = {0};
ll data[100005], lend;
ll n, m, t, ans;
void getprim()
{
    ll i, j, k;
    for(i = 2; i <= 100000; i++)
    {
        if(isprim[i] == 0)
        {
            prim[lenp++] = i;
            for(j = 2; j * i <= 100000; j++)
            {
                isprim[j * i] = 1;
            }
        }
    }
}
void getnum(ll n)
{
    ll i, j, k;
    lend = 0;
    for(i = 0; prim[i] * prim[i] <= n; i++)
    {
        if(n % prim[i] == 0)
        {
            data[lend++] = prim[i];
            while(n % prim[i] == 0)n /= prim[i];
        }
    }
    if(n != 1)data[lend++] = n;
}
void dfs(ll x, ll sum, ll num)
{
    if(num > lend)return ;
    if(num % 2 == 1)ans += m / sum;
    else ans -= m / sum;
    for(ll i = x + 1; i < lend; i++)
    {
        dfs(i, sum * data[i], num + 1);
    }
}
int main()
{
    getprim();
    scanf("%lld", &t);
    while(t--)
    {
        scanf("%lld %lld", &n, &m);
        ll i, j, k;
        ans = 0;
        for(i = 1; i <= n; i++)
        {
            getnum(i);
            for(j = 0; j < lend; j++)
            {
                dfs(j, data[j], 1);
            }
        }
        printf("%lld\n", n * m - ans);
    }
    return 0;
}