题解 | #数制转换#

#include <iostream>
#include <cstring>
#include <vector>
using namespace std;
int char2int(char x){
    if(x>='a'&&x<='f') return x-'a'+10;
    else if(x>='A'&&x<='F') return x-'A'+10;
    else if(x>='0'&& x<='9') return x-'0';
    else return -1;
}
char int2char(int x){
    if(x>=0 && x<=9) return x+'0';
    else return x-10+'A';
}
int main() {
    int b1,b2;
    string x;
    while(cin>>b1>>x>>b2){
        long long n=0;
        int i=0;
        while(x[i]=='0') i++;
        while(i<x.length()){
            n=n*b1+char2int(x[i]);
            i++;
        }
        vector<char> arr;
        if(n==0) {
            cout<<n<<endl;
            continue;}
        while(n>0){
            arr.push_back(int2char(n%b2));
            n/=b2;
        }
        for(int i=arr.size()-1;i>=0;i--) cout<<arr[i];
        cout<<endl;

    }

}