BZOJ 4407 于神之怒加强版

http://www.lydsy.com/JudgeOnline/problem.php?id=4407

题意:

给下N,M,K.求

思路:

 来自:http://blog.csdn.net/ws_yzy/article/details/50670213

#include<cstdio>
#include<cmath>
#include<iostream>
#include<algorithm>
#include<cstring>
#define ll long long
const ll Mod=1000000007;
ll f[5000005],sum[5000005],p[5000005],s[5000005];
bool mark[5000005];
ll K,n,m;
ll read(){
    ll t=0,f=1;char ch=getchar();
    while (ch<'0'||'9'<ch){if (ch=='-') f=-1;ch=getchar();}
    while ('0'<=ch&&ch<='9'){t=t*10+ch-'0';ch=getchar();}
    return t*f;
}
ll Pow(ll x,ll y){
    ll res=1;
    while (y){
        if (y%2) res=(res*x)%Mod;
        y/=2;
        x=(x*x)%Mod;
    }
    return res;
}
void init(){
    f[1]=1;
    for (int i=2;i<=5000000;i++){
        if (!mark[i]){
            p[++p[0]]=i;
            s[p[0]]=Pow(i,K);
            f[i]=s[p[0]]-1;
        }
        for (int j=1;j<=p[0]&&p[j]*i<=5000000;j++){
            mark[p[j]*i]=1;
            if (i%p[j]==0){
                f[i*p[j]]=f[i]*s[j]%Mod;
                break;
            }
            f[i*p[j]]=f[i]*f[p[j]]%Mod;
        }
    }
    for (int i=1;i<=5000000;i++)
     sum[i]=sum[i-1]+f[i]%Mod;
}
int main(){
    int T=read();K=read();
    init();
    while (T--){
        n=read();m=read();
        if (n>m) std::swap(n,m);
        int j=1;
        ll ans=0;
        for (int i=1;i<=n;i=j+1){
            j=std::min(n/(n/i),m/(m/i));
            ans+=(((n/i)*(m/i)%Mod)*(sum[j]-sum[i-1]))%Mod;
            ans%=Mod;
        }
        printf("%lld\n",ans);
    }
    return 0;
}