题解 | 识别有效的IP地址和掩码并进行分类统计

正则表达式

#include <bitset>
#include <iostream>
#include <iterator>
#include <regex>
#include <sstream>
#include <string>
#include <vector>
using namespace std;
static regex ipRex(
        R"(^((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$)");
static regex maskRex(
        R"(^((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$)");
bool isValidIP(const string& ip) {
    return regex_match(ip, ipRex);
}

bool isValidMask(const string& mask) {
    if (!regex_match(mask, maskRex)) return false;

    // mask转二进制
    stringstream ss(mask);
    string segment;
    unsigned long binaryMask = 0;
    while (getline(ss, segment, '.')) {
        binaryMask = (binaryMask << 8) | stoi(segment);
    }

    // 判断mask合法
    bitset<32> bit(binaryMask);
    bool zero = false;
    for (int i = 31; i >= 0; --i) {
        if (!bit.test(i)) {
            zero = true;
        } else if (zero) {
            return false;
        }
    }

    return !(binaryMask == 0 || binaryMask == 0xFFFFFFFF);
}

bool isPrivateIP(const string& ip) {
    stringstream ss(ip);
    string segment;
    unsigned long binaryip = 0;
    while (getline(ss, segment, '.')) {
        binaryip = (binaryip << 8) | stoi(segment);
    }

    return (binaryip >= 0x0A000000 && binaryip <= 0x0AFFFFFF) ||
           // 10.0.0.0-10.255.255.255
           (binaryip >= 0xAC100000 && binaryip <= 0xAC1FFFFF) ||
           // 172.16.0.0-172.31.255.255
           (binaryip >= 0xC0A80000 &&
            binaryip <= 0xC0A8FFFF);    // 192.168.0.0-192.168.255.255
}

int main() {
    string a;
    string sub = "~";
    int pos = 0;
    vector<pair<string, string>> temp;
    vector<int> res(7, 0); // A B C D E error privateIP

    while (cin >> a) {
        if ((pos = a.find(sub)) != string::npos) {
            temp.emplace_back(a.substr(0, pos), a.substr(pos + 1, a.size() - 1));
        }
    }

    for (auto it : temp) {
        string ip = it.first;
        string mask = it.second;
        // "0.*.*.*" 和 "127.*.*.*" 的 IP 地址跳过分类
        if (ip.find("0.") == 0 || ip.find("127.") == 0) {
            continue;  
        }
        if (!isValidIP(ip) || !isValidMask(mask)) {
            res[5]++;
            continue;
        }

        stringstream ss(ip);
        string segment;
        unsigned long binaryip = 0;
        while (getline(ss, segment, '.')) {
            binaryip = (binaryip << 8) | stoi(segment);
        }

        if(binaryip >= 0x01000000 && binaryip <= 0x7EFFFFFF){       //A类："1.0.0.0"-"126.255.255.255"
            res[0]++;
            if(isPrivateIP(ip)) res[6]++;
        }else if (binaryip >= 0x80000000 && binaryip <= 0xBFFFFFFF) { //B类："128.0.0.0"-"191.255.255.255"
            res[1]++;
            if(isPrivateIP(ip)) res[6]++;
        }else if (binaryip >= 0xC0000000 && binaryip <= 0xDFFFFFFF) { //C类："192.0.0.0"-"223.255.255.255"
            res[2]++;
            if(isPrivateIP(ip)) res[6]++;
        }else if (binaryip >= 0xE0000000 && binaryip <= 0xEFFFFFFF) { //D类："224.0.0.0"-"239.255.255.255"
            res[3]++;
        }else if (binaryip >= 0xF0000000 && binaryip <= 0xFFFFFFFF) {  //D类："240.0.0.0"-"255.255.255.255"
            res[4]++;
        }
    }

    for (auto num : res) {
        cout << num << ' ';
    }
    cout << endl;
    return 0;
}