修改后的代码

#include <iostream>
#include <vector>
#include <string>

using namespace std;

// 将数字转换为对应进制字符
char radixForm(int num) {
    return num < 10 ? num + '0' : (num - 10) + 'a';
}

// 将字符转换为对应数字
int radixForm(char ch) {
    return ch <= '9' ? ch - '0' : ch - 'A' + 10;
}

// 去除字符串开头的0
string legalizedNumStr(const string& s, int radix) {
    int i = 0;
    while (i < s.length() && s[i] == '0') {
        i++;
    }
    string newStr = s.substr(i);
    if (newStr.empty()) {
        newStr = "0";
    }
    for (char ch : newStr) {
        if (radix <= radixForm(ch)) {
            return "0";
        }
    }
    return newStr;
}

// 任意进制转换
string radixConvert(const string& os, int oldRadix, int newRadix) {
    string s = legalizedNumStr(os, oldRadix);
    if (s == "0") {
        return s;
    }
    vector<int> num(s.length());
    for (int i = 0; i < s.length(); i++) {
        num[i] = radixForm(s[i]);
    }
    vector<int> result;
    while (true) {
        int remainder = 0;
        vector<int> quotient;
        for (int i = 0; i < num.size(); i++) {
            int current = remainder * oldRadix + num[i];
            quotient.push_back(current / newRadix);
            remainder = current % newRadix;
        }
        result.push_back(remainder);
        int i = 0;
        while (i < quotient.size() && quotient[i] == 0) {
            i++;
        }
        num.assign(quotient.begin() + i, quotient.end());
        if (num.empty()) {
            break;
        }
    }
    string bs;
    for (int i = result.size() - 1; i >= 0; i--) {
        bs += radixForm(result[i]);
    }
    return bs;
}

int main() {
    int ra1, ra2;
    string a;
    cin >> ra1 >> ra2;
    cin >> a;
    string ans = radixConvert(a, ra1, ra2);
    cout << ans << endl;
    return 0;
}