1010.Radix (25) 溢出

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
string n1, n2;

long long get_num(char &c){
    if(isdigit(c)) return c - '0';
    else return c - 'a' + 10;
}
long long get_n(long long &r, string &n){
    long long s = 0;
    for (int i = 0; i < n.size(); i++) {
        s = s * r + get_num(n[i]);
    }
    return s;
}

int main(){
    long long tag, radix;
    cin >> n1 >> n2 >> tag >> radix;
    if(tag == 2) swap(n1, n2);
    long long num1 = get_n(radix, n1);
    long long left = 2, right = num1 + 1;
    for (int i = 0; i < n2.size(); i++) {
        left = max(left, get_num(n2[i])+1);
    }
    while (left <= right) {
        long long mid = (left + right) / 2;
        long long num2 = get_n(mid, n2);
        if(num2 > num1 || num2 < 0){
            right = mid - 1;
        }else if(num1 == num2){
            cout << mid << endl;
            return 0;
        }else{
            left = mid + 1;
        }
    }
    cout << "Impossible\n";
    return 0;
}