使用bitset、string、to_string、stoi等实现反转

#include <bits/stdc++.h>
using namespace std;
char biconvert(char c) {
    bitset<4> bs(stoi(string("0X") + c, 0, 16));
    string s(bs.to_string());
    reverse(s.begin(), s.end());
    int i = stoi(s, nullptr, 2);
    if (i < 10) {
        return i + '0';
    } else {
        return i + 'A' - 10;
    }
}
int main() {
    string s1, s2;
    cin >> s1 >> s2;
    string s;
    // first step
    s = s1 + s2;
    // second step
    s1.clear();
    s2.clear();
    for (int i = 0; i < s.size(); i = i + 2) {
        s1 += s[i];
    }
    for (int i = 1; i < s.size(); i = i + 2) {
        s2 += s[i];
    }
    sort(s1.begin(), s1.end());
    sort(s2.begin(), s2.end());
    s.clear();
    size_t short_len = min(s1.size(), s2.size());
    for (int i = 0; i < short_len; ++i) {
        s += s1[i];
        s += s2[i];
    }
    if (s1.size() > s2.size()) {
        for (int i = short_len; i < s1.size(); ++i) {
            s += s1[i];
        }
    } else {
        for (int i = short_len; i < s2.size(); ++i) {
            s += s2[i];
        }
    }
    // third step
    for (int i = 0; i < s.size(); ++i) {
        if (isdigit(s[i]) || s[i] >= 'a' && s[i] <= 'f' || s[i]  >= 'A' && s[i] <= 'F') {
            s[i] = biconvert(s[i]);
        }
    }
    cout << s << endl;
}