暴力搜会超时所以要用二分搜索

#include <bits/stdc++.h>
using namespace std;
using f=long long;
unordered_map<char,int> Jinwei;
f trans(char *s,f radix){
    f result =0;
    for (int i = 0; s[i] !='\0' ; ++i) {
        result=result*radix+Jinwei[s[i]];
    }
    return result;
}
f findRadix(char *n1,char*n2,f radix){
    f right=trans(n1,radix),left=-1;
    f tag=trans(n1,radix);
    for (int i = 0; n2[i] !='\0' ; ++i) {
        left=max(left,(f)Jinwei[n2[i]]+1);
    }
    while (left<right){
        f mid=left+(right-left)/2,k=trans(n2,mid);
        if (k<0 or k>=tag)
            right=mid;
        else if (k<tag)
            left=mid+1;
    }
    if (trans(n2,left)!=tag)
        return -1;
    return left;
}
int main(){
    char N1[11],N2[11];
    f tag,radix;
    scanf("%s %s%lld%lld",N1,N2,&tag,&radix);
    for (int i = 0; i < 36; ++i) {
        Jinwei.insert({i<10?i+'0':i-10+'a',i});
    }
    radix=tag==1?findRadix(N1,N2,radix):findRadix(N2,N1,radix);
    if (radix==-1)
        printf("Impossible");
    else
        printf("%lld",radix);
    return 0;
}