题解 | #合法IP#

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

bool isnum(string& s){
    int n = 0;
    if(s.empty()) return false;
    else if(s.size()>=2&&s[0]=='0') return false;
    for(int i=0;i<s.size();i++){
        if(!isdigit(s[i])) return false;
        n = n*10+s[i]-'0';
    }
    if(n>=0&&n<=255) return true;
    else return false;
}

int main() {
    string s;
    while (getline(cin, s)) {
        stringstream ss(s);
        string str;
        int ret = true;
        int cnt = 0;
        while(getline(ss, str, '.')){
            ret&=isnum(str);
            cnt++;
        }
        if(cnt!=4) ret = false;
        cout<<(ret?"YES":"NO");
    }
}

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