题解 | 识别有效的IP地址和掩码并进行分类统计

#include<iostream>
#include<string>
#include<sstream>
#include<vector>
using namespace std;

int  judge_ip(string ip){
    int j = 0;
    istringstream iss(ip);
    string seg;
    while(getline(iss,seg,'.'))
        
    {
        if(j==0&&(stoi(seg)==127||stoi(seg)==0))return 0;
        if(++j > 4 || seg.empty() || stoi(seg) > 255)
            return -1;
    }
    return 1;
}

bool is_private(string ip){
    istringstream iss(ip);
    string seg;
    vector<int> v;
    while(getline(iss,seg,'.')) v.push_back(stoi(seg));
    if(v[0] == 10) return true;
    if(v[0] == 172 && (v[1] >= 16 && v[1] <= 31)) return true;
    if(v[0] == 192 && v[1] == 168) return true;
    return false;
}

bool is_mask(string ip){
    istringstream iss(ip);
    string seg;
    unsigned b = 0;
    while(getline(iss,seg,'.')) b = (b << 8) + stoi(seg);
    if(!b) return false;
    b = ~b + 1;
    if(b == 1) return false;
    if((b & (b-1)) == 0) return true;
    return false;
}

int main(){
    string input;
    int a = 0,b = 0,c = 0,d = 0,e = 0,err = 0,p = 0;
    while(cin >> input){
        istringstream is(input);
        string add;
        vector<string> v;
        while(getline(is,add,'~')) v.push_back(add);
        if(judge_ip(v[0])==1 && !is_mask(v[1]))
            err++;
        else{
            if(judge_ip(v[0])==-1)
                err++;
            else{
                int first = stoi(v[0].substr(0,v[0].find_first_of('.')));
                if(is_private(v[0])) p++;
                if(first > 0 && first <127) a++;
                else if(first > 127 && first <192) b++;
                else if(first > 191 && first <224) c++;
                else if(first > 223 && first <240) d++;
                else if(first > 239 && first <256) e++;
            }
        }
    }
    cout << a << " " << b << " " << c << " " << d << " " << e << " " << err << " " << p << endl;
    return 0;
}