题解 | #合法IP#

#include <cstdio>
#include <iostream>
#include <regex>
#include <string>
using namespace std;

int main() {
    
    string input;
    cin >> input;

    string match = R"([\d]{1,3}\.[\d]{1,3}\.[\d]{1,3}\.[\d]{1,3})";
    regex reg_match(match);
    if(!regex_match(input, reg_match))
    {
        puts("NO");
        return 0;
    }

    string sep = R"([.])";
    regex reg(sep);
    sregex_token_iterator iter(input.cbegin(), input.cend(), reg, -1);
    sregex_token_iterator end;
    for(; iter != end; ++ iter)
    {
        if(iter->str().length() > 1 && iter->str()[0] == '0') //前倒0
        {
            puts("NO");
            return 0;
        }
        if(stoi(iter->str()) > 255 || stoi(iter->str()) < 0)
        {
            puts("NO");
            return 0;
        }

    }

    puts("YES");
    return 0;
    
    return 0;
}
// 64 位输出请用 printf("%lld")