解题思路：

（1）判断范围

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

void helper(string &s) {
    vector<int> v;
    int i=0;
    string str="";
    while(i<s.length()) {
        if(s[i]!='.') {
            while(s[i]!='.') {
                str+=s[i];
                i++;
            }
            v.push_back(stoi(str));
            str="";
        } else {
            i++;
        }
    }
    
    for(int i=0;i<v.size();i++) {
        if(v[i]>255 || v[i]<0) {
            cout<<"NO"<<endl;
            return;
        }
    }
    cout<<"YES"<<endl;
    return;
}

int main() {
    string s;
    while(cin>>s) {
        helper(s);
    }
    return 0;
}