题解 | #整数与IP地址间的转换#

#include <algorithm>
#include <cctype>
#include <iostream>
#include <string>
#include <vector>
#include <sstream>
using namespace std;
//利用大数除法做进制转换；
string mTransTon(int m, string s, int n) {
    int remain, len = s.size();
    string res = "";
    for (int i = 0; i < len; ) {
        remain = 0;
        for (int j = i; j < len; j ++) {
            int temp = (remain * m + s[j] - '0') % n;
            s[j] = (remain * m + s[j] - '0') / n + '0';
            remain = temp;
        }
        res += char(remain + '0');
        while (s[i] == '0') i++;
    }
    reverse(res.begin(), res.end());
    return res;
}

string binTransToDec(string bin) {
    bin += '.';
    string subStr;
    vector<string> f;
    for (char c : bin) {
        if (isdigit(c)) {
            subStr += c;
        } else if (c == '.') {
            f.push_back(subStr);
            subStr.clear();
        }
    }
    string res;
    for (auto it = f.begin(); it != f.end(); it ++) {
        string sub = *it;
        sub = mTransTon(10, *it, 2);
        while (sub.size() < 8) sub = '0' + sub;
        res += sub;
    }
    res = mTransTon(2, res, 10);
    return res;
}

string decTransToBin(string dec) {
    
    string binIP = mTransTon(10, dec, 2);
    while (binIP.size() < 32) binIP = '0' + binIP;

    vector<string> vec;
    string subStr;
    for (int i = 1; i <= binIP.size(); i++) {
        if(i % 8 != 0) {
            subStr += binIP[i-1];
        }
        else if(i % 8 == 0 && subStr.size()){
            subStr += binIP[i-1];
            vec.push_back(subStr);
            subStr = "";
        }
    }
    string res;
    string subIP;
    for (auto it = vec.begin(); it != vec.end(); it ++) {
        subIP = mTransTon(2, *it, 10);
        res += subIP;
        res += '.';
    }
    res.erase(res.end() - 1);
    return res;
}

int main() {
    string bin, dec;
    cin >> bin;
    cin >> dec;

    string transedBin = binTransToDec(bin);
    cout << transedBin << endl;
    string transedDec = decTransToBin(dec);
    cout << transedDec << endl;

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