题解 | #判断两个IP是否属于同一子网#

这个掩码判断合法性有点难度，我已经忘了补码了，计组太恶心了。用了bitset模板

#include <algorithm>
#include <vector>
#include <bitset>
#include <cmath>
#include <sstream>

using namespace std;

bool judgeip(const vector<string> &v){
    int cnt = 0,x;
    for(int i = 0;i<4;i++){
        x = stoi(v[i]);
        if(x>=0&&(x<=255)){
            cnt++;
        }
    }
    if(cnt==4)return true;
    else return false;
}

unsigned long long mytransform(const vector<string> &v){
    unsigned long long x = 0;
    x+=stoi(v[0])*pow(2,24);
    x+=stoi(v[1])*pow(2,16);
    x+=stoi(v[2])*pow(2,8);
    x+=stoi(v[3]);
    return x;
}

bool judgemask(const vector<string> &v){
    bool mask =false;
    mask = judgeip(v);
    if(!mask)return mask;
    unsigned long long x= mytransform(v);
    unsigned long long y =~x+1;
   
    x=(x&(~x+1))+x;//血坑,位与运算比加法优先级低，这里找了好久的bug
    bitset<32> b(x);//unsigned long long 是64位的我们只判断低32位。
    if(b.count()==0)return true;
    else return false;
    
    
}




int main() {
    string str1,str2,str3;
    while(cin>>str1>>str2>>str3){
        vector<string> v1,v2,v3;
        
        string temp;
        stringstream s1,s2,s3;
        s1.str(str1);
        while(getline(s1,temp,'.')){
            v1.push_back(temp);
        }
        s2.str(str2);
        while(getline(s2,temp,'.')){
            v2.push_back(temp);
        }
        s3.str(str3);
        while(getline(s3,temp,'.')){
            v3.push_back(temp);
        }
        bool samenet = false,correct = false;
        correct = judgemask(v1)&&judgeip(v2)&&judgeip(v3);
        if(!correct) cout<<1<<endl;
        else {
            unsigned long long masknet = mytransform(v1);
            unsigned long long x = mytransform(v2);
            unsigned long long y = mytransform(v3);
            unsigned long long mx = x&masknet;
            unsigned long long my = y&masknet;
            if(mx==my)samenet = true;
            if(samenet)cout<<0<<endl;
            else cout<<2<<endl;
        }
        
        
    }
}