Java and Smalltalk solutions for Wk 147 Task 1

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diff --git a/challenge-147/cheok-yin-fung/java/LeftTruncatablePrime.java b/challenge-147/cheok-yin-fung/java/LeftTruncatablePrime.java
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+// The Weekly Challenge 147
+// Task 1 Truncatable Prime
+// Friday, January 14, 2022 AM11:26:14 HKT
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.Arrays;
+@SuppressWarnings("unchecked")
+
+public class LeftTruncatablePrime
+{
+    public static List<Integer> Primes;
+    public static List<Integer> LTPrimes;
+    public static List<Integer> recentLTPrimes;
+    public static List<Integer> newLTPrimes;
+
+    public static void main(String... args) 
+    {
+        Integer[] singleDigitPrimes = {2, 3, 5, 7};
+        Primes = new ArrayList<Integer>();
+        Collections.addAll(Primes, singleDigitPrimes);
+
+        LTPrimes = new ArrayList<Integer>();
+        recentLTPrimes = new ArrayList<Integer>();
+        Collections.addAll(recentLTPrimes, singleDigitPrimes);
+        newLTPrimes = new ArrayList<Integer>();
+        appendPrimes(1000);
+        appendLTPrimes(20);
+        
+        for (int i = 0; i < 20; i++)
+            System.out.println(LTPrimes.get(i));
+    }
+
+    public static boolean isPrime(Integer x)
+    {
+        Integer p = 0;
+        for (int i = 0; p <= Math.sqrt(x) ; i++ )
+        {
+            p = Primes.get(i);
+            if (x % p == 0) 
+                return false;
+        } 
+        return true;
+    }
+
+    public static void appendPrimes(Integer max)
+    {
+        Integer i = Primes.get(Primes.size()-1)+1;
+        while (Primes.get(Primes.size()-1) < max)
+        {
+            if (isPrime(i))
+                Primes.add(i);
+            i++;
+        }
+    }
+
+
+    public static void appendLTPrimes(Integer targetSize)
+    {
+        if (targetSize <= LTPrimes.size() + recentLTPrimes.size())
+        {
+            LTPrimes.addAll(recentLTPrimes);
+            return;
+        }
+        for (int d = 1; d <= 9; d++) {
+            for (Integer num : recentLTPrimes)
+            {
+                int newNum = Integer.parseInt(d + "" + num);
+                if (isPrime(newNum)) {
+                    newLTPrimes.add(newNum);
+                }
+            }
+        }
+        LTPrimes.addAll(recentLTPrimes);
+        recentLTPrimes = (List)((ArrayList)newLTPrimes).clone();
+        newLTPrimes.clear();
+        appendLTPrimes(targetSize);
+    }
+}