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 <bitset>
#include <math.h>

using namespace std;
typedef long long int ll;

int a = 0, b = 0, c = 0, d = 0, e = 0, err = 0, p = 0;

bool ziwangyanma(int z[]) {
    //按位取反加一后正好为2^n则为正确掩码
    //在十进制下就是2^(n+1)-X正好是2^i
    unsigned int ipy = 0;
    ipy = z[3] + z[2] * 256 + z[1] * 65536 + z[0] * 16777216;
    ipy = 4294967296 - ipy;
    for (int i = 1; i < 32; ++i) {
        if (ipy - (int)pow(2, i) == 0) {
            return true;
        }
    }
    err++;
    return false;
}

int main() {
    cin.tie(0);
    cout.tie(0);
    ios::sync_with_stdio(0);
    string ip_input;
here:
    while (getline(cin, ip_input)) {
        if (ip_input.empty())break;
        int ip[4] = { 0, 0, 0, 0 }; // IP地址
        int ipy[4] = { 0, 0, 0, 0 }; // 掩码地址
        string temp[8];
        for (int i = 0, j = 0; i < ip_input.length(); i++) {
            if (ip_input[i] != '.' && ip_input[i] != '~') {
                temp[j] += ip_input[i];
            } else j++;
        }
        for (int i = 0, m = 0, n = 0; i < 8; i++) {
            if (temp[i].size() == 0) {
                err++;
                goto here;
            } else {
                if (i <= 3) {// IP存放
                    ip[m] = stoi(temp[i]);
                    m++;
                } else { // 掩码存放
                    ipy[n] = stoi(temp[i]);
                    n++;
                }
            }

        }
        if (ip[0] == 0 || ip[0] == 127) {
            goto here;
        }
        //先看子网掩码
        if (ziwangyanma(ipy)) {
            //IP可忽略错误
            for (int i = 0; i < 4; i++) {
                if (ip[i] < 0 || ip[i] > 255) {
                    err++;
                    goto here;
                }
            }
            //A~E统计
            if (ip[0] >= 1 && ip[0] <= 126) {
                a++;
                if (ip[0] == 10)p++;
            } else if (ip[0] >= 128 && ip[0] <= 191) {
                b++;
                if (ip[0] == 172 && ip[1] >= 16 && ip[1] <= 31)p++;
            } else if (ip[0] >= 192 && ip[0] <= 223) {
                c++;
                if (ip[1] == 168)p++;
            } else if (ip[0] >= 224 && ip[0] <= 239) {
                d++;
            } else if (ip[0] >= 240 && ip[0] <= 255) {
                e++;
            }
        }
    }
    cout << a << ' ' << b << ' ' << c << ' ' << d << ' ' << e << ' ' << err << ' '
         << p;
    return 0;
}

就是很多判断语句的一个算法，也没想出其他新鲜的操作了。