题解 | #判断两个IP是否属于同一子网#

#include<string>
#include<vector>
using namespace std;
class Solution{
public:
    int get_ans(string &mask,string IP1,string IP2){
        vector<int> mask_4(4),IP1_4(4),IP2_4(4);
       // cout<<mask<<' '<<IP1<<' '<<IP2<<endl;
        //以下数值化子网掩码，IP1和IP2
        int i=0,index=0;
        while(index<4){
            mask_4[index++]=get_num(mask,i);
        }
        i=0,index=0;
        while(index<4){
            IP1_4[index++]=get_num(IP1,i);
        }
        i=0,index=0;
        while(index<4){
            IP2_4[index++]=get_num(IP2,i);
        }
        //判断
        int res=0;
        for(int i=0;i<4;i++){
            //超出255范围
            if(mask_4[i]>255||IP1_4[i]>255||IP2_4[i]>255){
                return 1;
            }
            //子网掩码到此开始后面是0
            if(mask_4[i]!=255){
                if(mask_4[i]!=0&&mask_4[i]!=0x80&&mask_4[i]!=0xC0&&mask_4[i]!=0xE0
                  &&mask_4[i]!=0xF0&&mask_4[i]!=0xF8&&mask_4[i]!=0xFC&&mask_4[i]!=0xFE){
                    return 1;
                }
                
                for(int j=i+1;j<4;j++){
                    if(mask_4[j]!=0){
                        return 1;
                    }
                }
            }
            //cout<<(IP1_4[i]&mask_4[i])<<' '<<(IP2_4[i]&mask_4[i])<<endl;
            //判断两IP是或否为同一网络的子网
            if((IP1_4[i]&mask_4[i])!=(IP2_4[i]&mask_4[i])){
                res=2;
            }
        }
        return res;
        
    }
    int get_num(string &s,int &i){
        int res=0;
        while(i<s.size()&&s[i]!='.'){
            //特殊字符，返回256
            if(s[i]<'0'||s[i]>'9'){
                return 256;
            }
            res*=10;
            res+=s[i++]-'0';
        }
        i++;
        return res;
    }
};
int main(){
    string mask,IP1,IP2;
    Solution sol;
    while(cin>>mask>>IP1>>IP2){
        cout<<sol.get_ans(mask,IP1,IP2)<<endl;
    }
    
    return 0;
    
}