题解 | #合法IP#

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

int main() {
    string s;
    cin>>s;
    if(s[0] == '.'){
        cout << "NO"<<endl;
        return 0;
    }
    int count =0;
    int cur_s = 0;
    for (int i=0; i<s.size(); i++) {
        if (s[i] == '.' && s[i+1] !='.') {
            string t = s.substr(cur_s,i-cur_s);
            count = count + 1;
            cur_s = i+1;
            if(t.size() == 0 || stoi(t)> 255) {
                cout << "NO"<<endl;
                return 0;            
            }
            if(t.size()>1 && t[0]=='0'){
                cout << "NO"<<endl;
                return 0;
            }
        }
        else if (s[i]>='0' && s[i]<='9') {
            continue;
        }
        else {
            cout <<"NO"<<endl; 
            return 0;
        }
    }
    string t = s.substr(cur_s, s.size()- cur_s);
    if(t.size() == 0 || stoi(t)> 255){
        cout << "NO"<<endl;
        return 0;  
    }else if(t.size()>1 && t[0] == '0'){
        cout << "NO"<<endl;
        return 0;
    }else {
     count = count + 1;
    }
    if(count == 4){
        cout << "YES" <<endl;
        return 0;
    }else {
        cout <<"NO"<<endl;
        return 0;
    }

}
// 64 位输出请用 printf("%lld")