codeforces 17 D Notepad 快速冪？

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題意：求((b-1)*bn-1)%c　　b和n都很大很大

#include <iostream>#include <stdio.h>#include <string.h>#include <math.h>#include <algorithm>#include <string>#include <map>#include <queue>#include <stack>#include <vector>using namespace std;#define LL long longchar b[1000005],n[1000005];int main(){    int i,j,k,m,len1,len2,c;    LL tp,ans,x;    while(scanf(" %s %s %d",b,n,&c)!=EOF)    {        len1=strlen(b);        x=0;        for(i=0; i<len1; i++)        {            x=x*10+b[i]-‘0‘;            x%=c;        }        ans=x-1;        if(ans<0) ans+=c;        len2=strlen(n);        for(i=len2-1; i>=0; i--)        {            if(n[i]>‘0‘)            {                n[i]--;                break;            }            n[i]=‘9‘;        }        for(i=len2-1; i>=0; i--)        {            tp=x;            for(j=1; j<=9; j++)            {                if(j==n[i]-‘0‘) ans*=x;                x*=tp;                x%=c;            }            ans%=c;        }        if(ans==0) ans=c;        printf("%lld\n",ans);    }    return 0;}

 

codeforces 17 D Notepad 快速冪？