题解 | #识别有效的IP地址和掩码并进行分类统计#

用到正则表达式来简化代码，先判断掩码是否正确，然后判断IP地址是否正确，最终输出统计结果。

#include <iostream>
#include <regex>
#include <cmath>
using namespace std;

void analysisAddr(vector<int> & nums, string s);
void judgePri(const vector<int> & nums, int & pri_addr);

int main() {
    regex regex("\\d+\\.\\d+\\.\\d+\\.\\d+~\\d+\\.\\d+\\.\\d+\\.\\d+");
    string s;
    int A = 0;
    int B = 0;
    int C = 0;
    int D = 0;
    int E = 0;
    int mistake = 0;
    int pri_addr = 0;
    string ip;
    string host;
    vector<int> nums;
    int num;
    bool flag = true;
    bool conti = false;
    bool high = false;
    while (getline(cin, s)) {
        if(!regex_match(s, regex)) {
            mistake++;
            continue;
        };
        ip = s.substr(0, s.find('~'));
        host = s.substr(s.find('~') + 1);
        nums.clear();
        analysisAddr(nums, ip);
        if (nums.at(0) == 0 || nums.at(0) == 127) {
            continue;
        }
        nums.clear();
        analysisAddr(nums, host);
        if (nums.at(0) == 0 || nums.at(3) == 255) {
            mistake++;
            continue;
        }
        for (int num : nums) {
            if (flag == false) {
                if (num != 0) {
                    mistake++;
                    conti = true;
                    flag = true;
                    break;
                }
            } else {
                if (num != 255) {
                    flag = false;
                    if (high == true && num == 0) {
                        continue;
                    }
                    if (num != 254 && num != 252 && num != 248 && num != 240 && num != 224 && num != 192 && num != 128) {
                        mistake++;
                        conti = true;
                        break;
                    }
                } else {
                    high = true;
                }
            }
        }
        flag = true;
        high = false;
        if (conti == true) {
            conti = false;
            continue;
        }
        nums.clear();
        analysisAddr(nums, ip);
        if (nums.at(0) >= 1 && nums.at(0) <= 126 && nums.at(1) < 256 && nums.at(2) < 256 && nums.at(3) < 256) {
            A++;
            judgePri(nums, pri_addr);
            continue;
        } else if (nums.at(0) >= 128 && nums.at(0) <= 191 && nums.at(1) < 256 && nums.at(2) < 256 && nums.at(3) < 256) {
            B++;
            judgePri(nums, pri_addr);
            continue;
        } else if (nums.at(0) >= 192 && nums.at(0) <= 223 && nums.at(1) < 256 && nums.at(2) < 256 && nums.at(3) < 256) {
            C++;
            judgePri(nums, pri_addr);
            continue;
        } else if (nums.at(0) >= 224 && nums.at(0) <= 239 && nums.at(1) < 256 && nums.at(2) < 256 && nums.at(3) < 256) {
            D++;
            continue;
        } else if (nums.at(0) >= 240 && nums.at(0) <= 255 && nums.at(1) < 256 && nums.at(2) < 256 && nums.at(3) < 256) {
            E++;
            continue;
        }
        if (nums.at(0) == 0 || nums.at(0) == 127) {
            continue;
        }
        mistake++;
    }
    cout << A << ' ' << B << ' ' << C << ' ' << D << ' ' << E << ' ' << mistake << ' ' << pri_addr;
}

void analysisAddr(vector<int> & nums, string s) {
    int start = 0;
    int end;
    end = s.find('.');
    while (true) {
        end = s.find('.', start);
        if (s.find('.', start) == string::npos) {
            nums.push_back(stoi(s.substr(start)));
            break;
        }
        nums.push_back(stoi(s.substr(start, end - start)));
        start = end + 1;
    }
}

void judgePri(const vector<int> & nums, int & pri_addr) {
    if (nums.at(0) == 10 && nums.at(0) <= 255 && nums.at(1) < 256 && nums.at(2) < 256 && nums.at(3) < 256) {
        pri_addr++;
    }
    if (nums.at(0) == 172 && nums.at(1) >= 16 && nums.at(1) <= 31 && nums.at(2) < 256 && nums.at(3) < 256) {
        pri_addr++;
    }
    if (nums.at(0) == 192 && nums.at(1) == 168 && nums.at(2) < 256 && nums.at(3) < 256) {
        pri_addr++;
    }
}
// 64 位输出请用 printf("%lld")