Practice date and time stuff

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diff --git a/challenge-038/cheok-yin-fung/README.md b/challenge-038/cheok-yin-fung/README.md
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+Goals:
+  
+- Java: Get familiar with the Date and Time API, 
+- Perl: Get familiar with Time::Piece (and Time::Seconds) module, especially the strftime and strptime methods
+
+attempt on 9th May, 2021
diff --git a/challenge-038/cheok-yin-fung/java/DateFinder.java b/challenge-038/cheok-yin-fung/java/DateFinder.java
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+++ b/challenge-038/cheok-yin-fung/java/DateFinder.java
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+// The Weekly Challenge - 038 
+// Task 1 Date Finder
+// attempt: May 09th, 2021
+// from: C.-Y. Fung
+// Usage: java DateFinder [7-digit string]
+
+import java.time.LocalDate;
+import java.time.YearMonth;
+
+public class DateFinder
+{
+    public static void main(String[] args) 
+    {
+        String myYear = "", in_str = "";
+        try {
+            in_str = args[0];
+            for (char numChar : in_str.toCharArray()) {
+                if (numChar < '0' || numChar> '9') {
+                    System.out.println("Non-numeric character found.");
+                    throw new IllegalArgumentException();
+                }
+            }
+            switch(in_str.charAt(0)) {
+                case '1': myYear = "20"+in_str.substring(1,3); break;
+                case '2': myYear = "19"+in_str.substring(1,3); break;
+                default: throw new IllegalArgumentException();
+            }
+            if (in_str.length() != 7) { 
+                System.out.println("Input digits is not equal to 7.");
+                throw new IllegalArgumentException();
+            }
+        } catch (IllegalArgumentException e) {
+            System.out.println("Ilegal argument.");
+            System.exit(0);
+        } catch (IndexOutOfBoundsException e) {
+            System.out.println("Usage: java DateFinder [7-digit string]");
+            System.exit(0);
+        }
+
+        String myMonth = in_str.substring(3,5);
+        int myMonth_i = Integer.parseInt(myMonth);
+        try {
+            if (myMonth_i > 12 || myMonth_i < 1) 
+                throw new IllegalArgumentException();
+        } catch (IllegalArgumentException e) {
+            System.out.println("Problem in Month (within 01-12) " + myMonth);
+            System.exit(0);
+        }
+        String myDay = in_str.substring(5,7);
+        int myDay_i = Integer.parseInt(myDay);
+        int myYear_i = Integer.parseInt(myYear);
+        try {
+            YearMonth temp = YearMonth.of(myYear_i, myMonth_i);
+            int daysInMonth = temp.lengthOfMonth();
+            if (myDay_i > daysInMonth || myDay_i < 1) 
+                throw new IllegalArgumentException();
+        } catch (IllegalArgumentException e) {
+            System.out.println("Problem in date (last two digits) " + myDay);
+            System.exit(0);
+        } finally {
+            System.out.println(myYear + "-" + myMonth + "-" + myDay);        
+        }
+    }
+
+}
diff --git a/challenge-038/cheok-yin-fung/perl/ch-1.pl b/challenge-038/cheok-yin-fung/perl/ch-1.pl
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+#!/usr/bin/perl
+# The Weekly Challenge - 038 
+# Task 1 Date Finder
+# attempt: May 09th, 2021
+# from: C.-Y. Fung
+# Usage: ch-1.pl [7-digit string]
+# Java correspondence: DateFinder.java
+use Time::Piece;
+use strict;
+use warnings;
+
+my $str = $ARGV[0] || die "A 7-digit string is expected.";
+die "Format Error: A 7-digit string is expected." if length $str != 7;
+
+$str =~ s/^1/20/;
+$str =~ s/^2/19/;
+die "Error: first digit must be 1 or 2! " if $str =~ /[^12]/;
+
+my $Y = substr($str, 0, 4);
+my $Month = substr($str, 4, 2);
+my $d = substr($str, 6, 2);
+
+die "Problem in month ($Month)! " 
+    if $Month > 12 || $Month < 1;
+my $check = Time::Piece->strptime(substr($str,0,6)."01" , "%Y%m%d"); 
+die "Problem in date (last two digits: $d)! " 
+    if $d > $check->month_last_day || $d < 1;
+
+my $t = Time::Piece->strptime($str, "%Y%m%d"); 
+
+
+print $t->strftime("%Y-%m-%d"), "\n";