题解 | #判断两个IP是否属于同一子网#

#include <cctype>
#include <iostream>
#include <bits/stdc++.h>
#include <vector>
using namespace std;
vector<string> add_(string s){
    vector<string> vec;
    string tmp;
    for (int i = 0; i < s.size(); i++) {
        if (i == s.size() - 1 ) {
            tmp += s[i];
            vec.push_back(tmp);
        }
        if (s[i] == '.' && !tmp.empty()) {
            vec.push_back(tmp);
            tmp = "";
        } else {
            tmp += s[i];
        }
    }
    return vec;
}
bool check_(vector<string> vec) {
    //四个部分
    if (vec.size() != 4) {
        return false;
    }
    for (auto it : vec) {
        //数字
        for (auto ch : it) {
            if (!isdigit(ch))
                return false;
        }
        //0在数字前
        int num_index = 0;
        if (it.size() > 1) {
            for (auto ch : it) {
                if (ch == '0' && num_index == 0)
                    return false;
                if (ch != '0')
                    num_index = 1;
            }
        }
        if (stoi(it) < 0 || stoi(it) > 255)
            return false;
    }
    return true;
}
bool check_mask(vector<string> vec){
    string tmp;
    for (auto it : vec){
        int n = stoi(it);
        bitset<8> foo(n);
        tmp += foo.to_string();
    }
    int num_index = 0;
    for (auto it : tmp){
        if (it != '1')
            num_index = 1;
        if (it == '1' && num_index == 1)
            return false;
    }
    return true;
}
bitset<32> erwei(vector<string> v){
    string str = "";
    for (auto it : v){
        int n = stoi(it);
        bitset<8> foo(n);
        str += foo.to_string();
    }
    //cout << str.size();
    //long long m = stol(str);
    bitset<32> foo(str);
    //cout << foo<<endl;
    return foo;
}
bool check_ip(vector<string> v_m,vector<string> v_1,vector<string> v_2){
    bitset<32> foo_1 = erwei(v_1);
    bitset<32> foo_2 = erwei(v_2);
    bitset<32> foo_m = erwei(v_m);
    if ((foo_1 & foo_m ) == (foo_2 & foo_m ))
        return true;
    return false;
}
int main() {
    string mask, ip_1, ip_2;
    while (cin >> mask >> ip_1 >> ip_2){
        int index = 0;
        vector<string> v_m = add_(mask);
        vector<string> v_1 = add_(ip_1);
        vector<string> v_2 = add_(ip_2);
        if (!check_(v_1) || !check_(v_2) || !check_(v_m) || !check_mask(v_m)){
            cout<<'1'<<endl;
            continue;
        }
        if (check_ip(v_m, v_1, v_2)){
            cout<<"0"<<endl;
            continue;
        }
        cout << '2'<<endl;
    }
}
// 64 位输出请用 printf("%lld")