题解 | 进制转换

#include <iostream>
using namespace std;
using ll_t = long long;

ll_t toDex(const string& str){
    string hex_num_str = str.substr(2);
    ll_t sum = 0;

    for (char ch : hex_num_str) {
        if (ch >= 'A' && ch <= 'F') {
            sum = sum*16 + ch - 'A' + 10;
        } else {
            sum = sum*16 + ch - '0';
        }
    }

    return sum;
}

int main() {
    string hex;
    cin >> hex;

    ll_t num = toDex(hex);

    cout << num << endl;
    return 0;
}
// 64 位输出请用 printf("%lld")