题解 | #识别有效的IP地址和掩码并进行分类统计#

#include <iostream>
#include <bits/stdc++.h>
#include <vector>
using namespace std;
vector<string> add_(string s){
    vector<string> vec;
    string tmp;
    for (int i = 0; i < s.size(); i++) {
        if (i == s.size() - 1 ) {
            tmp += s[i];
            vec.push_back(tmp);
        }
        if (s[i] == '.' && !tmp.empty()) {
            vec.push_back(tmp);
            tmp = "";
        } else {
            tmp += s[i];
        }
    }
    return vec;
}
bool check_ip(vector<string> vec) {
    //四个部分
    if (vec.size() != 4) {
        return false;
    }
    for (auto it : vec) {
        //数字
        for (auto ch : it) {
            if (!isdigit(ch))
                return false;
        }
        //0在数字前
        int num_index = 0;
        if (it.size() > 1) {
            for (auto ch : it) {
                if (ch == '0' && num_index == 0)
                    return false;
                if (ch != '0')
                    num_index = 1;
            }
        }
        if (stoi(it) < 0 || stoi(it) > 255)
            return false;
    }
    return true;
}
bool check_mask(vector<string> vec){
    if (!check_ip(vec))
        return false;
    string tmp;
    for (auto it : vec){
        int n = stoi(it);
        bitset<8> foo(n);
        tmp += foo.to_string();
    }
    int zero_index = 0;
    int one_index = 0;
    for (auto it : tmp){
        if (it == '1')
            one_index = 1;
        if (it == '0')
            zero_index = 1;
        if (it == '1' && zero_index == 1)
            return false;
    }
    //只有0/1
    if ((one_index == 1 && zero_index == 0) || (one_index == 0 && zero_index == 1))
        return false;
    return true;
}
int main() {
    string str;
    int A = 0,B = 0,C = 0,D = 0,E = 0,erro = 0,self = 0;
    while(cin>>str){
        string ip, mask;
        for (int i = 0; i < str.size(); i++){
            if (str[i] == '~'){
                ip = str.substr(0, i);
                mask = str.substr(i + 1, str.size() - i - 1);
            }
        }
        vector<string> v_ip = add_(ip);
        vector<string> v_mask = add_(mask);
        //特殊
        if (v_ip[0] == "0"|| v_ip[0] == "127")  continue;
        //erro
        if (!check_ip(v_ip) || !check_mask(v_mask)){
            erro++;
            continue;
        }
        //私网
        if (v_ip[0] == "10"){
            self++;
            //continue;
        }
        if (v_ip[0] == "192" && v_ip[1] == "168"){
            self++;
            //continue;
        }
        if (v_ip[0] == "172" && (stoi(v_ip[1]) >= 16 && stoi(v_ip[1]) <= 31)){
            self++;
            //continue;
        }
        //abcde
        int n = stoi(v_ip[0]);
        if (n <= 126){
            A++;
            continue;
        }
        else if (n <= 191){
            B++;
            continue;
        }
        else if (n <= 223){
            C++;
            continue;
        }
        else if (n <= 239){
            D++;
            continue;
        }
        else{
            E++;
            continue;
        }
    }
    cout<<A<<' '<<B<<' '<<C<<' '<<D<<' '<<E<<' '<<erro<<' '<<self;
}
// 64 位输出请用 printf("%lld")