Philips and Calculator

代码

#include<cstdio>
#include<algorithm>
using namespace std;

const int N = 3 * 1e6;
int l , r , p , tp , prime[105] , num[N + 5] , n , vis[105] , f[N + 5] , ok[N + 5] , ans;

inline void getp()
{
    vis[1] = vis[0] = 1;
    for(register int i = 2; i <= p; i++)
    {
        if (!vis[i]) prime[++tp] = i;
        for(register int j = 1; j <= tp && prime[j] * i <= p; j++)
        {
            vis[i * prime[j]] = 1;
            if (i % prime[j] == 0) break;
        }
    }
}

inline void dfs(int x , int v)
{
    num[++n] = v;
    for(register int i = x; i <= tp; i++)
    if (prime[i] * (long long)v <= r) dfs(i , prime[i] * v);
}

int main()
{
    scanf("%d%d%d" , &l , &r , &p);
    getp();
    dfs(1 , 1);
    num[++n] = 1;
    sort(num + 1 , num + n + 1);
    f[1] = 0;
    for(register int i = 2; i <= n; i++) f[i] = 1e9;
    for(register int i = 2; i <= p; i++)
    {
        register int j = 1;
        for(register int k = 1; k <= n; k++)
        {
            while (j <= n && num[k] * i != num[j]) j++;
            if (j > n) break;
            if (f[k] + 1 < f[j]) f[j] = f[k] + 1;
            if (f[j] + i <= p && num[j] >= l && !ok[j]) ok[j] = 1 , ans++;
        }
    }
    printf("%d" , ans);