模拟

import java.io.*;
import java.util.*;
public class Main{
    public static void main(String[] args) throws Exception {
        BufferedReader sc=new BufferedReader(new InputStreamReader(System.in));
        String s[]=sc.readLine().split("/");
        int a=Integer.parseInt(s[0]);
        int b=Integer.parseInt(s[1]);
        int c=Integer.parseInt(s[2]);
        String s1="";
        String s2="";
        String s3="";
        if(a<60) s1="20"+s[0]+"-"+s[1]+"-"+s[2];
        else s1="19"+s[0]+"-"+s[1]+"-"+s[2];
        if(c<60){ 
            s2="20"+s[2]+"-"+s[0]+"-"+s[1];
            s3="20"+s[2]+"-"+s[1]+"-"+s[0];
        }
        else {
            s2="19"+s[2]+"-"+s[0]+"-"+s[1];
            s3="19"+s[2]+"-"+s[1]+"-"+s[0];
        }

        boolean f1=false,f2=false,f3=false;

        Set<String> sum=new TreeSet<>();
        sum.add(s1);
        sum.add(s2);
        sum.add(s3);


        if(b>=1&&b<=12&&check(a,b,c)) f1=true;
        if(a>=1&&a<=12&&check(c,a,b)) f2=true;
        if(b>=1&&b<=12&&check(c,b,a)) f3=true;

        for(String t:sum){
            if(t.equals(s1)&&f1) System.out.println(t);
            else if(t.equals(s2)&&f2) System.out.println(t);
            else if(t.equals(s3)&&f3) System.out.println(t);
        }

    }
    static int days[]={0,31,28,31,30,31,30,31,31,30,31,30,31};
    static boolean check(int year,int mouth,int day){
        if(year<60) year+=2000;
        else year+=1900;
        if(mouth!=2) if(day<1||day>days[mouth]) return false;
        if(mouth==2){
            int append=0;
            if(year%400==0||(year%100!=0&&year%4==0)) append=1;
            if(day>days[mouth]+append) return false;
        }
        return true;
    }
}

枚举

import java.io.*;
public class Main{
    public static void main(String[] args) throws Exception {
        BufferedReader sc=new BufferedReader(new InputStreamReader(System.in));
        String s[]=sc.readLine().split("/");
        sc.close();
        int a=Integer.parseInt(s[0]);
        int b=Integer.parseInt(s[1]);
        int c=Integer.parseInt(s[2]);

        for(int i=19600101;i<=20591231;i++){

            int year=i/10000, mouth=i%10000/100,day=i%100;
            if(check(year,mouth,day)) {
            if(((year%100)==a&&mouth==b&&day==c)||
               ((year%100)==c&&mouth==a&&day==b)||
               ((year%100)==c&&mouth==b&&day==a))
                System.out.printf("%02d-%02d-%02d\n",year,mouth,day);
            }
        }

    }
    static int days[]={0,31,28,31,30,31,30,31,31,30,31,30,31};
    static boolean check(int year,int mouth,int day){
        if(mouth<1||mouth>12) return false;
        if(day<1) return false;
        if(mouth!=2){
            if(day>days[mouth]) return false;
        }else{
            int leap=0;
            if(year%400==0||(year%100!=0&&year%4==0)) leap=1;
            if(day>days[mouth]+leap) return false;
        }
        return true;
    }
}