In the given year, there will be only one palindromic date. Hence, to find previous palindromic date, you need to decrements the year and convert it to palindromic date.
Example: for 2030, valid month and day will be 03 and 02 which will lead to 2030/03/02.
So, it must be clear that palindromic date in this case is only possible when:
Year is of 4 digits (not for 10000) as months and number of days are in two digits
Last two digits of years might be {10, 20, 30, 40, 50, 60, 70, 80, 90, 01, 11, 21}
First two digits of years should be mirror image of 1-31 (with month and year validity).
Using rule 2 and 3, it can be checked in O(1) whether a given year has palindromic date or not in the given format. Let us assume that valid range of year is from 9999-0001, then it can be done in linear order to find previous palindromic date.
- package com.kartik.date.palindrome;
import java.util.GregorianCalendar;
public class DatePalindrome {
public static void main(String[] args) {
String date = "1001/10/01";
System.out.println("Enter date is --"+date);
System.out.println("----->>>Given Date previous Palindrome<<<--- ");
System.out.println("YYYY/DD/MM");
findPrevDate(date);
System.out.println("----->>>Given Date Next Palindrome<<<--- ");
System.out.println("YYYY/DD/MM");
findNextDate(date);
}
static void findPrevDate(String input) {
int year = extractYear(input); // Extract first 4 digits
--year;
// limit is 101 because 0000 will not give you valid month and day.
for (; year >= 101; --year) {
if (hasPalindromic(year)) {
writeDate(year);
}
}
}
static void findNextDate(String input) {
int year = extractYear(input);
--year;
for (; year <= 9999; ++year) {
if (hasPalindromic(year)) {
writeDate(year);
}
}
}
static boolean hasPalindromic(int year) {
int first2 = year % 100;
int last2 = year / 100;
boolean second_valid = false;
boolean first_valid = false;
switch (last2) {
case 10:
case 20:
case 30:
case 40:
case 50:
case 60:
case 70:
case 80:
case 90:
case 1:
case 11:
case 21:
second_valid = true;
break;
}
if (!second_valid)
return false;
switch (first2) {
case 10:
case 20:
case 30:
case 40:
case 50:
case 60:
case 70:
case 80:
case 90:
case 1:
case 11:
case 21:
case 31:
case 41:
case 51:
case 61:
case 71:
case 81:
case 91:
case 2:
case 12:
case 22:
case 32:
case 42:
case 52:
case 62:
case 72:
case 82:
case 92:
case 3:
case 13:
first_valid = true;
break;
}
if (!first_valid)
return false;
// reverse digit such that 2 yields 20
int month = reverseDigitsOn100(last2);
int day = reverseDigitsOn100(first2);
GregorianCalendar cal = (GregorianCalendar) GregorianCalendar
.getInstance();
if (month == 2) {
if (day <= 28)
return true;
if (cal.isLeapYear(year) && day == 29)
return true;
if (day > 28)
return false;
}
switch (month) {
case 4:
case 6:
case 9:
case 11:
if (day > 30)
return false;
}
// For remaining months, check is already made as first part of year is
// gives day in range of [1..31].
return true;
}
static int reverseDigitsOn100(int n) {
int r = 0;
if (n == 0)
return 0;
r = r * 10;
r = r + n % 10;
reverseDigitsOn100(n / 10);
return r;
}
static long reverse(int number) {
int reversedNumber = 0;
int temp = 0;
while (number > 0) {
temp = number % 10;
reversedNumber = reversedNumber * 10 + temp;
number = number / 10;
}
return reversedNumber;
}
static int extractYear(String input) {
return Integer.parseInt(input.substring(0, 4));
}
static void writeDate(int input) {
long rev = reverse(input);
String reverseYear = String.valueOf(rev);
if (String.valueOf(input).length() < 4) {
reverseYear = reverseYear + "0";
}
if (reverseYear.length() < 4) {
reverseYear = "0" + reverseYear;
}
String dd = reverseYear.substring(0, 2);
String mm = reverseYear.substring(2, 4);
StringBuffer br = new StringBuffer();
br.append(input);
br.append('/');
br.append(dd);
br.append('/');
br.append(mm);
System.out.println(br.toString());
}
}
- Enter date is --1001/10/01
----->>>Given Date previous Palindrome<<<---
YYYY/DD/MM
192/29/10
191/19/10
190/09/10
182/28/10
181/18/10
180/08/10
172/27/10
171/17/10
170/07/10
162/26/10
161/16/10
160/06/10
152/25/10
151/15/10
150/05/10
142/24/10
141/14/10
140/04/10
132/23/10
131/13/10
130/03/10
122/22/10
121/12/10
120/02/10
113/31/10
112/21/10
111/11/10
110/01/10
103/30/10
102/20/10
101/10/10
----->>>Given Date Next Palindrome<<<---
YYYY/DD/MM
1001/10/01
1002/20/01
1003/30/01
1010/01/01
1011/11/01
1012/21/01
1013/31/01
1020/02/01
1021/12/01
1022/22/01
1030/03/01
1031/13/01
1032/23/01
1040/04/01
1041/14/01
1042/24/01
1050/05/01
1051/15/01
1052/25/01
1060/06/01
1061/16/01
1062/26/01
1070/07/01
1071/17/01
1072/27/01
1080/08/01
1081/18/01
1082/28/01
1090/09/01
1091/19/01
1092/29/01
1101/10/11
1102/20/11
1103/30/11
1110/01/11
1111/11/11
1112/21/11
1113/31/11
1120/02/11
1121/12/11
1122/22/11
1130/03/11
1131/13/11
1132/23/11
1140/04/11
1141/14/11
1142/24/11
1150/05/11
1151/15/11
1152/25/11
1160/06/11
1161/16/11
1162/26/11
1170/07/11
1171/17/11
1172/27/11
1180/08/11
1181/18/11
1182/28/11
1190/09/11
1191/19/11
1192/29/11
2001/10/02
2002/20/02
2003/30/02
2010/01/02
2011/11/02
2012/21/02
2013/31/02
2020/02/02
2021/12/02
2022/22/02
2030/03/02
2031/13/02
2032/23/02
2040/04/02
2041/14/02
2042/24/02
2050/05/02
2051/15/02
2052/25/02
2060/06/02
2061/16/02
2062/26/02
2070/07/02
2071/17/02
2072/27/02
2080/08/02
2081/18/02
2082/28/02
2090/09/02
2091/19/02
2092/29/02
2101/10/12
2102/20/12
2103/30/12
2110/01/12
2111/11/12
2112/21/12
2113/31/12
2120/02/12
2121/12/12
2122/22/12
2130/03/12
2131/13/12
2132/23/12
2140/04/12
2141/14/12
2142/24/12
2150/05/12
2151/15/12
2152/25/12
2160/06/12
2161/16/12
2162/26/12
2170/07/12
2171/17/12
2172/27/12
2180/08/12
2181/18/12
2182/28/12
2190/09/12
2191/19/12
2192/29/12
3001/10/03
3002/20/03
3003/30/03
3010/01/03
3011/11/03
3012/21/03
3013/31/03
3020/02/03
3021/12/03
3022/22/03
3030/03/03
3031/13/03
3032/23/03
3040/04/03
3041/14/03
3042/24/03
3050/05/03
3051/15/03
3052/25/03
3060/06/03
3061/16/03
3062/26/03
3070/07/03
3071/17/03
3072/27/03
3080/08/03
3081/18/03
3082/28/03
3090/09/03
3091/19/03
3092/29/03
4001/10/04
4002/20/04
4003/30/04
4010/01/04
4011/11/04
4012/21/04
4013/31/04
4020/02/04
4021/12/04
4022/22/04
4030/03/04
4031/13/04
4032/23/04
4040/04/04
4041/14/04
4042/24/04
4050/05/04
4051/15/04
4052/25/04
4060/06/04
4061/16/04
4062/26/04
4070/07/04
4071/17/04
4072/27/04
4080/08/04
4081/18/04
4082/28/04
4090/09/04
4091/19/04
4092/29/04
5001/10/05
5002/20/05
5003/30/05
5010/01/05
5011/11/05
5012/21/05
5013/31/05
5020/02/05
5021/12/05
5022/22/05
5030/03/05
5031/13/05
5032/23/05
5040/04/05
5041/14/05
5042/24/05
5050/05/05
5051/15/05
5052/25/05
5060/06/05
5061/16/05
5062/26/05
5070/07/05
5071/17/05
5072/27/05
5080/08/05
5081/18/05
5082/28/05
5090/09/05
5091/19/05
5092/29/05
6001/10/06
6002/20/06
6003/30/06
6010/01/06
6011/11/06
6012/21/06
6013/31/06
6020/02/06
6021/12/06
6022/22/06
6030/03/06
6031/13/06
6032/23/06
6040/04/06
6041/14/06
6042/24/06
6050/05/06
6051/15/06
6052/25/06
6060/06/06
6061/16/06
6062/26/06
6070/07/06
6071/17/06
6072/27/06
6080/08/06
6081/18/06
6082/28/06
6090/09/06
6091/19/06
6092/29/06
7001/10/07
7002/20/07
7003/30/07
7010/01/07
7011/11/07
7012/21/07
7013/31/07
7020/02/07
7021/12/07
7022/22/07
7030/03/07
7031/13/07
7032/23/07
7040/04/07
7041/14/07
7042/24/07
7050/05/07
7051/15/07
7052/25/07
7060/06/07
7061/16/07
7062/26/07
7070/07/07
7071/17/07
7072/27/07
7080/08/07
7081/18/07
7082/28/07
7090/09/07
7091/19/07
7092/29/07
8001/10/08
8002/20/08
8003/30/08
8010/01/08
8011/11/08
8012/21/08
8013/31/08
8020/02/08
8021/12/08
8022/22/08
8030/03/08
8031/13/08
8032/23/08
8040/04/08
8041/14/08
8042/24/08
8050/05/08
8051/15/08
8052/25/08
8060/06/08
8061/16/08
8062/26/08
8070/07/08
8071/17/08
8072/27/08
8080/08/08
8081/18/08
8082/28/08
8090/09/08
8091/19/08
8092/29/08
9001/10/09
9002/20/09
9003/30/09
9010/01/09
9011/11/09
9012/21/09
9013/31/09
9020/02/09
9021/12/09
9022/22/09
9030/03/09
9031/13/09
9032/23/09
9040/04/09
9041/14/09
9042/24/09
9050/05/09
9051/15/09
9052/25/09
9060/06/09
9061/16/09
9062/26/09
9070/07/09
9071/17/09
9072/27/09
9080/08/09
9081/18/09
9082/28/09
9090/09/09
9091/19/09
9092/29/09
I am Kartik Chandra Mandal from Bangalore, India. Working as software engineer in Java technology. Have good knowledge of OWASP and CSRF in security for applications and it's implementation in Java technology.