题解 | #识别有效的IP地址和掩码并进行分类统计#

//https://www.nowcoder.com/practice/de538edd6f7e4bc3a5689723a7435682?tpId=37&tqId=21241&rp=1&ru=/exam/oj/ta&qru=/exam/oj/ta&sourceUrl=%2Fexam%2Foj%2Fta%3FtpId%3D37&difficulty=undefined&judgeStatus=undefined&tags=&title=

#include <iostream>
#include <string.h>
#include <sstream>
#include <vector>
#include <bitset>
#include <algorithm>

using namespace std;

int isip(string ip){
    stringstream ss(ip);
    vector<string> num;

    while(getline(ss, ip, '.'))
        num.push_back(ip);

    if(num.size()!=4)
        return 0;

    for(auto c:num){
        int ctem = stoi(c);
        if(0>ctem||ctem>255||c.size()==0)
            return 0;
    }

    return 1;
}

int ismask(string mask){
    if(isip(mask)){
        if(mask=="255.255.255.255"||mask=="0.0.0.0")
            return 0;

        stringstream ss(mask);
        string num;

        while(getline(ss, mask, '.')){
            bitset<8> bit(stoi(mask));
            num+=bit.to_string();
        }

        int pos0 = num.find("0");
        reverse(num.begin(), num.end());
        int pos1 = num.find("1");

        if((pos1+pos0)==32)
            return 1;
        else
            return 0;

    }else
        return 0;
}

int isprivate(string ip){
    stringstream ss(ip);
    vector<string> num;

    while(getline(ss, ip, '.'))
        num.push_back(ip);

    if(num[0]=="10")
        return 1;
    if((num[0]=="172")&&(16<=stoi(num[1])&&(stoi(num[1])<=31)))
        return 1;
    if(num[0]=="192"&&num[1]=="168")
        return 1;
    return 0;
}

int main() {
    string s;
    int ans[7];
    memset(ans, 0, sizeof(ans));

    while (getline(cin, s)) {
        string ip, mask;
        stringstream ss(s);
        getline(ss, ip, '~');
        getline(ss, mask, '~');

        if(isip(ip)){
            if(stoi(ip)==0||stoi(ip)==127)
                continue;
            if(ismask(mask)){
                if(isprivate(ip))
                    ans[6]++;

                int ntem = stoi(ip);

                if(1<=ntem&&ntem<=126)
                   ans[0]++;
                if(128<=ntem&&ntem<=191)
                   ans[1]++;
                if(192<=ntem&&ntem<=223)
                   ans[2]++;
                if(224<=ntem&&ntem<=239)
                   ans[3]++;
                if(240<=ntem&&ntem<=255)
                   ans[4]++;
            }else
                ans[5]++;

        }else{
            ans[5]++;
        }


    }

    for(auto c:ans)
        cout << c << ' ';
}