题解 | #进制转换#

#include <iostream>
using namespace std;
// a的b次方
int pow(int a, int b) {
    if (b == 0) return 1;
    if (b == 1) return a;

    if (b % 2 == 0) return pow(a * a, b / 2);
    else return a * pow(a, b - 1);
}
int main() {
    string s;
    int ans = 0;
    cin >> s;
    int cnt = 0;
    for (int i = s.size() - 1; i >= 2; i--) {
        if ('0' <= s[i] && s[i] <= '9') ans += (s[i] - '0') * pow(16, cnt);
        else ans += (s[i] - 'A' + 10) * pow(16, cnt);
        cnt++;
    }
    cout << ans << endl;
}