回文日期

#include<bits/stdc++.h>
using namespace std;

int y[2][13] = {{0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
                {0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}};

int is_r(int x){  //判断是否是闰年
    if((x % 4 == 0 && x % 100 != 0) || (x % 100 == 0 && x % 400 == 0)) return 1;
    else return 0;
}

int Stoi(string s){  //蓝桥杯不支持将string转换为int类型的函数，手搓一个
    int sum = 0;
    for(int i = 0; i < s.size(); i ++){
        sum = sum * 10 + int(s[i] - '0');
    }
    return sum;
}

bool is_t(string x, int p){  //判断该年份是否合法，即月份和天数是否合法
    int sum = 0;
    int m = Stoi(x.substr(0, 2));
    int d = Stoi(x.substr(2, 2));
    if(m >= 1 && m <= 12 && d <= y[is_r(p)][m]) return 1;
    return 0;
}

string To_string(int num){  //蓝桥杯不支持将int转换为string类型的函数，手搓一个
    string sum = "";
    while(num){
        int t = num % 10;
        sum += char(t + '0');
        num /= 10;
    }
    reverse(sum.begin(), sum.end());
    return sum;
}

bool is_b(string a, string b){  //判断这一年是否在所给年份之后
    int m1 = Stoi(a.substr(0, 2)), m2 = Stoi(b.substr(0, 2));
    if(m1 == m2){
        int d1 = Stoi(a.substr(2, 2)), d2 = Stoi(b.substr(2, 2));
        return d1 > d2;
    }
    else return m1 > m2;
}

string to_y(int a, int b, int c){  //将年份化为0000-00-00这种形式
    string sum = "";
    string A = To_string(a);
    while(A.size() < 4) A = "0" + A;
    string B = To_string(b);
    while(B.size() < 2) B = "0" + B;
    string C = To_string(c);
    while(C.size() < 2) C = "0" + C;
    return A + B + C;
}

void solve(){

    string s; cin >> s;
    string t = s.substr(0, 4);  //取出年
    string k = s.substr(4, 4);  //取出月份和日期
    int year = Stoi(t);
    int Y = year;
    int m = Stoi(k.substr(0, 2));  //取出月份
    int d = Stoi(k.substr(2, 2));  //取出日期

    while(1){  //暴力枚举
        d ++;  //日期++
        if(d > y[is_r(Y)][m]){
            d = 1, m ++;  //超过该月的最大日期，月份++
        }
        if(m > 12) Y ++, m = 1;  //超过12月，年份++
        string s1 = to_y(Y, m, d);  //转化为 0000-00-00 的形式
        string s2 = s1; 
        reverse(s2.begin(), s2.end());
        if(s1 == s2){  //判断是否回文
            cout << s1 << endl;
            break;
        }
    }

    string ab = s.substr(0, 2);
    int yy = Stoi(ab);  //ABABBABA形，先取出AB
    for(int i = 0; ; i ++){
        int Y = yy + i;
        string a = To_string(Y);
        if(a[0] == a[1]) continue;  //AA直接跳过
        a += a;  //得到ABAB
        string aa = a;
        reverse(a.begin(), a.end());  //月份和日期必须为BABA
        int b = Stoi(a);
        if(is_t(a, Y) && (is_b(a, k) || is_b(aa, t))){
            cout << aa << a << endl;
            break;
        }
    }
}

int main(){
    solve();
    return 0;
}