题解 | 验证IP地址

按照题目中的规则将 ip 地址重新生成一遍：

#include <string>
#include <vector>
#include <array>
#include <cstdio>
#include <algorithm>
#include <cctype>
#include <sstream>
#include <iomanip>

std::vector<std::string> Split(const std::string& str, char delimiter) {
    std::vector<std::string> result;
    std::size_t start = 0, end = 0;
    std::string token;
    while ((end = str.find(delimiter, start)) != std::string::npos) {
        token = str.substr(start, end - start);
        result.push_back(std::move(token));
        start = end + 1;
    }
    result.push_back(str.substr(start));
    return result;
}

std::string Join(const std::vector<std::string>& strs, char delimiter) {
    if (strs.empty()) {
        return "";
    }
    std::string result = strs[0];
    for (int i=1; i<strs.size(); ++i) {
        result += delimiter + strs[i];
    }
    return result;
}

std::string MakeIPv4(const std::array<int, 4>& nums, char delimiter) {
    if (nums.empty()) {
        return "";
    }
    std::string result = std::to_string(nums[0]);
    for (int i=1; i<nums.size(); ++i) {
        result += delimiter + std::to_string(nums[i]);
    }
    return result;
}

std::string MakeIpv6(const std::array<int, 8>& nums, char delimiter) {
    if (nums.empty()) {
        return "";
    }
    std::stringstream ss;
    ss << std::hex << std::uppercase << std::setfill('0') << std::setw(4) << nums[0];
    for (int i=1; i<nums.size(); ++i) {
        ss << delimiter  << std::setfill('0') << std::setw(4) << nums[i];
    }
    return ss.str();
}

class Solution {
  public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 验证IP地址
     * @param IP string字符串 一个IP地址字符串
     * @return string字符串
     */
    string solve(string IP) {
        // write code here
        if (IP[1] == '.' || IP[2] == '.' || IP[3] == '.') {
            std::array<int, 4> ip;
            if (sscanf(IP.c_str(), "%d.%d.%d.%d", &ip[0], &ip[1], &ip[2], &ip[3]) == 4) {
                if (ip[0] < 256 && ip[1] < 256 && ip[2] < 256 && ip[3] < 256) {
                    std::string newIP = MakeIPv4(ip, '.');
                    if (newIP == IP) {
                        return "IPv4";
                    }
                }
            }
        } else if (IP[4] == ':') {
            std::vector<std::string> ipSegments = Split(IP, ':');
            if (ipSegments.size() == 8) {
                std::array<int, 8> ip;
                for (int i = 0; i < 8; ++i) {
                    std::string &ipSegment = ipSegments[i];
                    if (sscanf(ipSegment.c_str(), "%x", &ip[i])) {
                        switch(ipSegment.length()) {
                            case 1:
                                ipSegment = "000" + ipSegment;
                                break;
                            case 2:
                                ipSegment = "00" + ipSegment;
                                break;
                            case 3:
                                ipSegment = "0" + ipSegment;
                                break;
                            case 4:
                                break;
                            default:
                                return "Neither";
                        }
                    }
                }
                std::string formattedIP = Join(ipSegments, ':');
                std::transform(formattedIP.begin(), formattedIP.end(), formattedIP.begin(), ::toupper);
                std::string newIP = MakeIpv6(ip, ':');
                if (formattedIP == newIP) {
                    return "IPv6";
                }
            }
        }
        return "Neither";
    }
};