题解 | #判断两个IP是否属于同一子网#

#include <iostream>
#include <string>
#include <vector>
using namespace std;

int main() {
    string mask, ip1, ip2;
    while (cin >> mask >> ip1 >> ip2) { // 注意 while 处理多个 case
        vector<int> vmask;
        vector<int> vip1;
        vector<int> vip2;

        int n = 0;
        int ans = -1;
        for (auto c : mask) {
            if (c >= '0' && c <= '9') {
                n = n * 10 + (c - '0');
            }
            if (c == '.') {
                vmask.push_back(n);
                n = 0;
            }
            if(c == '-')
            ans = 1;
        }
        vmask.push_back(n);
        n = 0;
        for (auto c : ip1) {
            if (c >= '0' && c <= '9') {
                n = n * 10 + (c - '0');
            }
            if (c == '.') {
                vip1.push_back(n);
                n = 0;
            }
            if(c == '-')
            ans = 1;
        }
        vip1.push_back(n);
        n = 0;
        for (auto c : ip2) {
            if (c >= '0' && c <= '9') {
                n = n * 10 + (c - '0');
            }
            if (c == '.') {
                vip2.push_back(n);
                n = 0;
            }
            if(c == '-')
            ans = 1;
        }
        vip2.push_back(n);
        n = 0;

        
        if (vmask.size() != 4 || vip1.size() != 4 || vip2.size() != 4) {
            ans = 1;
            break;
        }
        for (int i = 0; i < 4; i++) {
            if (vmask[i] < 0 || vmask[i] > 255 || vip1[i] < 0 || vip1[i] > 255 ||
                    vip2[i] < 0 || vip2[i] > 255) {
                ans = 1;//格式非法
                break;
            }
        }
        for (int i = 0; i < 3; i++) { //掩码的网络号全为1，主机号全为0
            if (vmask[i] < 255 && vmask[i + 1] > 0) {
                ans = 1;
                break;
            }
        }

        if (ans == 1) { //格式非法，输出1
            cout << ans << endl;
        } else {
            for (int i = 0; i < 4; i++) {
                if ((vmask[i]&vip1[i]) !=
                        (vmask[i]&vip2[i])) { //两个ip地址和掩码做AND操作
                    ans = 2;
                    break;
                } else { //AND操作结果不相同
                    ans = 0;
                }
            }
            cout << ans << endl;
        }

    }
}
// 64 位输出请用 printf("%lld")