题解 | 回文日期

#include <algorithm>
#include <bits/stdc++.h>
#include <string>
using namespace std;
int day31[7] = {1, 3, 5, 7, 8, 10, 12};
int day30[4] = {4, 6, 9, 11};
bool run(int year) {
    return (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0);
}
bool p(string t,int endyear,int endmon,int endday,int styear,int stmon,int stday) {
    int year = stoi(t.substr(0, 4));
    int month = stoi(t.substr(4, 2));
    int day = stoi(t.substr(6, 2));
   if(year==styear){
        if(stmon>month){
            return false;
        }else if(stmon==month){
            if(stday>day){
                return false;
            }
        }
    }
    if(year==endyear){
        if(endmon<month){ 
            return false;
        }else if(endmon==month){
            //cout<<endyear<<" "<<endmon<<" "<<endday<<endl;
            if(endday>=day){
                return true;
            }else{
                return false;
            }
        }
    }
   if(month>12)return false;
   if(day>32)return false;
    //cout<<"|||"<<endl;
    if (month == 2) {
        if (run(year)) {
            if (day <= 29) {
                //cout<<t<<endl;
                return true;
            } else {
                 // cout<<t<<endl;
                return false;
            }
        } else {
            if (day <= 28) {
               // cout<<t<<endl;
                return true;
            } else {
                    //cout<<t<<endl;
                return false;
            }
        }
    } 
   //cout<<"|||"<<endl;
    for (auto it : day31) {
        if (it == month) {
            if (day <= 31) {
                //cout<<t<<endl;
                return true;
            } else {
                return false;
            }
        }
    }
    for (auto it : day30) {
        if (it == month) {
            if (day <= 30) {
               // cout<<t<<" "<<day<<endl;
                return true;
            } else {
                return false;
            }
        }
    } 
  
    return false;
}
int main() {
    string st, end;
    cin >> st;
    cin >> end;
    int styear = stoi(st.substr(0, 4));
     int stmon = stoi(st.substr(4, 2));
    int stday = stoi(st.substr(6, 2));
    int endyear = stoi(end.substr(0, 4));
    int endmon = stoi(end.substr(4, 2));
    int endday = stoi(end.substr(6, 2));
    int count = 0;
    for (int i = styear; i <= endyear; i++) {
        string s = to_string(i);
        string ans = s;
        reverse(s.begin(), s.end());
        ans += s;
      //cout<<ans<<endl;
        if (p(ans,endyear,endmon,endday,styear,stmon,stday))count++;
    }

    cout<<count;

}
// 64 位输出请用 printf("%lld")