Codeforces 906 D. Power Tower

http://codeforces.com/contest/906/problem/D

欧拉降幂

#include<cstdio>
#include<iostream>

using namespace std;

int pi[35],phi[35],lim;

int a[100001];

void read(int &x)
{
    x=0; char c=getchar();
    while(!isdigit(c)) c=getchar();
    while(isdigit(c)) { x=x*10+c-'0'; c=getchar(); }
}

int get_phi(int n)
{
    int ph=n;
    for(int i=2;i*i<=n;++i)
        if(!(n%i))
        {
            ph=ph/i*(i-1);
            while(!(n%i)) n/=i;
        }
    if(n>1) ph=ph/n*(n-1);
    return ph;
}

int Pow(int a,int b,int mod,bool &flag)
{
    int res=1;
    while(b)
    {
        if(b&1) 
        {
            flag|=(1LL*res*a>=mod);
            res=1LL*res*a%mod;    
        }
        flag|=(1LL*a*a>=mod);
        a=1LL*a*a%mod;
        b>>=1;
    }
    return res;
}

int f(int x,int dep)
{
    if(dep>lim)
    {
        x-=dep-lim;
        dep=lim;
    }
    if(dep==1) return a[x]%pi[1];
    int tmp=a[x]; 
    if(tmp>=phi[dep-1]) tmp=tmp%phi[dep-1]+phi[dep-1]; 
    x--; 
    bool flag;
    for(int i=dep-1;i;--i)
    {
        flag=false;
        tmp=Pow(a[x],tmp,pi[i],flag);
        if(flag) tmp+=phi[i-1];
        x--;
    }
    return tmp;
}

int main()
{
//    freopen("data.in","r",stdin);
//    freopen("my.out","w",stdout);
    int n,mod;
    read(n); read(mod);
    for(int i=1;i<=n;++i) read(a[i]);
    int tmp=mod;
    while(pi[lim]!=1)
    {
        pi[++lim]=tmp;
        phi[lim]=get_phi(tmp);
        tmp=phi[lim];
    }
    int q;
    read(q);
    int l,r;
    while(q--)
    {
        read(l); read(r);
        printf("%d
",f(r,r-l+1));
    }
    return 0;
}