- Added Java solution to the task "Truncatable Prime" of week 147.

1 files changed, 90 insertions, 0 deletions

diff --git a/challenge-147/mohammad-anwar/java/theweeklychallenge/TruncatablePrime.java b/challenge-147/mohammad-anwar/java/theweeklychallenge/TruncatablePrime.java
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+++ b/challenge-147/mohammad-anwar/java/theweeklychallenge/TruncatablePrime.java
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+package theweeklychallenge;
+
+/*
+
+Week 147:
+
+    https://theweeklychallenge.org/blog/perl-weekly-challenge-147
+
+Task #1: Truncatable Prime
+
+    Write a script to generate first 20 left-truncatable prime numbers in base 10.
+
+*/
+
+import java.lang.Math;
+import java.util.Arrays;
+import java.util.ArrayList;
+import junit.framework.TestCase;
+import java.util.regex.Pattern;
+import java.util.regex.Matcher;
+import static junit.framework.Assert.*;
+
+public class TruncatablePrime extends TestCase {
+
+    public static void main(String[] args) {
+        junit.textui.TestRunner.run(theweeklychallenge.TruncatablePrime.class);
+    }
+
+    public void testTruncatablePrime() {
+        Integer exp[] = {2, 3, 5, 7, 13, 17, 23, 37, 43, 47, 53, 67, 73, 83, 97, 113, 137, 167, 173, 197};
+        Integer got[] = leftTruncatablePrime(20);
+        assertTrue(Arrays.equals(exp, got));
+    }
+
+    public static Integer[] leftTruncatablePrime(int count) {
+        ArrayList<Integer> ltp = new ArrayList<Integer>();
+        int c = 0;
+        int n = 2;
+        while (c < count) {
+            String s = Integer.toString(n);
+
+            if (!Pattern.compile(".*0.*").matcher(s).matches() && isPrime(n)) {
+                Integer[] numbers = leftTruncatableNumbers(n);
+                boolean found = true;
+                if (numbers.length >=2) {
+                    for(int i = 0; i<numbers.length; i++) {
+                        if (!isPrime(numbers[i])) {
+                            found = false;
+                        }
+                    }
+                }
+                if (found) {
+                    ltp.add(n);
+                    c++;
+                }
+            }
+            n++;
+        }
+
+        Integer[] ltpArray = new Integer[ltp.size()];
+        return ltp.toArray(ltpArray);
+    }
+
+    public static Integer[] leftTruncatableNumbers(int n) {
+        int i = 0;
+        String s = Integer.toString(n);
+        ArrayList<Integer> numbers = new ArrayList<Integer>();
+        while (i < s.length()) {
+            numbers.add(Integer.valueOf(s.substring(i)));
+            i++;
+        }
+
+        Integer[] numArray = new Integer[numbers.size()];
+        return numbers.toArray(numArray);
+    }
+
+    public static boolean isPrime(int n) {
+        if (n == 1) {
+            return false;
+        }
+
+        for(int i=2; i <= Math.sqrt(n); i++) {
+            if ((n % i) == 0) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+}