1010. Radix (25)

#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <algorithm>

#include <string>
#include <cstring>
#include <vector>
#include <queue>

using namespace std;

string s1,s2;
int flag;
long long radix;
long long t;

long long Map[1000];
void init()
{
    for(char c='0';c<='9';c++)
    {
        Map[c]=c-'0';

    }
    for(char c='a';c<='z';c++)
    {
        Map[c]=c-'a'+10;
    }
}

long long to10(string s,long long radix)
{
    long long sum=0;
    int len=s.length();
    for(int i=0;i<len;i++)
    {
        sum=sum*radix+Map[s[i]];
    }

    return sum;
}

int findlow(string s)
{
    int mmax=0;
    int len=s.length();
    for(int i=0;i<len;i++)
    {
        if(Map[s[i]]>mmax)
        {
            mmax=Map[s[i]];
        }
    }

    return mmax+1;
}

int cmp(string s,long long radix,long long t)//s和t比较大小
{
    long long num=to10(s,radix);
    if(num<0)
       return 1;
    else if(num==t)
        return 0;
    else if(num<t)
        return -1;
    else
        return 1;
}

long long bisearch(string s,long long low,long long high)
{
    long long mid;
    while(low<=high)
    {
        mid=(low+high)/2;
        int flag=cmp(s,mid,t);
        if(flag==0)
            return mid;
        else if(flag==-1)//mid对应的值比t要小
            low=mid+1;
        else
            high=mid-1;
    }

    return -1;
}
int main()
{
    freopen("in.txt","r",stdin);

    init();//map
    cin>>s1>>s2>>flag>>radix;


    if(flag==2)
        swap(s1,s2);

    t=to10(s1,radix);
    long long low=findlow(s2);

    long long ans=bisearch(s2,low,t+1);


    if(ans==-1)
        printf("Impossible\n");
    else
        printf("%lld\n",ans);

    return 0;
}