Attempt p3 in Java

README.rst

@@ -85,7 +85,7 @@ Olivia's Project Euler Solutions
    |            |                            |        | |CodeQL| |br|     |
    |            |                            |        | |C#-lint|         |
    +------------+----------------------------+--------+-------------------+
-   | Java       | Java 8+ in Corretto, |br|  | 20     | |Javai| |br|      |
+   | Java       | Java 8+ in Corretto, |br|  | 21     | |Javai| |br|      |
    |            | Dragonwell, Liberica, |br| |        | |Ja-Cov| |br|     |
    |            | Microsoft, Oracle, |br|    |        | |CodeQL| |br|     |
    |            | Semeru, Temurin, & Zulu    |        | |Java-lint|       |

docs/index.rst

@@ -81,7 +81,7 @@ Problems Solved
   +-----------+-----------+------------+------------+------------+------------+------------+------------+------------+
   |:prob:`002`|:c-d:`0002`|:cp-d:`0002`|:cs-d:`0002`|:ja-d:`0002`|:js-d:`0002`|:lu-d:`0002`|:py-d:`0002`|:rs-d:`0002`|
   +-----------+-----------+------------+------------+------------+------------+------------+------------+------------+
-  |:prob:`003`|:c-d:`0003`|:cp-d:`0003`|:cs-d:`0003`|            |:js-d:`0003`|:lu-d:`0003`|:py-d:`0003`|:rs-d:`0003`|
+  |:prob:`003`|:c-d:`0003`|:cp-d:`0003`|:cs-d:`0003`|:ja-d:`0003`|:js-d:`0003`|:lu-d:`0003`|:py-d:`0003`|:rs-d:`0003`|
   +-----------+-----------+------------+------------+------------+------------+------------+------------+------------+
   |:prob:`004`|:c-d:`0004`|:cp-d:`0004`|:cs-d:`0004`|:ja-d:`0004`|:js-d:`0004`|:lu-d:`0004`|:py-d:`0004`|:rs-d:`0004`|
   +-----------+-----------+------------+------------+------------+------------+------------+------------+------------+

docs/src/java/lib/primes.rst

@@ -9,10 +9,14 @@ View source code :source:`java/src/main/java/euler/lib/Primes.java`
 
         :return: Iterates over the prime numbers
 
-    .. java:method:: public static Stream<Long> primesUntil(Long limit)
+    .. java:method:: public static Stream<Long> primesUntil(long limit)
 
         :return: Iterates over the prime numbers, up until a given limit
 
+    .. java:method:: public static Stream<Long> primeFactors(long target)
+
+        :return: Iterates over the prime factors of a number
+
 .. literalinclude:: ../../../../java/src/main/java/euler/lib/Primes.java
    :language: java
    :linenos:

docs/src/java/p0003.rst

@@ -0,0 +1,24 @@
+Java Implementation of Problem 3
+================================
+
+View source code :source:`java/src/main/java/euler/p0003.java`
+
+Includes
+--------
+
+- `Primes.java <./lib/primes.html>`_
+
+Problem Solution
+----------------
+
+.. java:type:: public class p0003 implements IEuler
+
+   .. java:method:: Object answer()
+
+    :return: The answer to Project Euler problem 3
+
+.. literalinclude:: ../../../java/src/main/java/euler/p0003.java
+   :language: java
+   :linenos:
+
+.. tags:: factorization, prime-number, java-iterator

java/README.rst

@@ -83,6 +83,7 @@ Problems Solved
 
 -  ☒ `1 <./src/main/java/p0001.java>`__
 -  ☒ `2 <./src/main/java/p0002.java>`__
+-  ☒ `3 <./src/main/java/p0003.java>`__
 -  ☒ `4 <./src/main/java/p0004.java>`__
 -  ☒ `6 <./src/main/java/p0006.java>`__
 -  ☒ `7 <./src/main/java/p0007.java>`__

java/src/main/java/euler/lib/Primes.java

@@ -30,7 +30,7 @@ public static Stream<Long> primes() {
         return StreamSupport.stream(new PrimeSpliterator(null), false);
     }
 
-    public static Stream<Long> primesUntil(Long limit) {
+    public static Stream<Long> primesUntil(long limit) {
         return StreamSupport.stream(new PrimeSpliterator(limit), false);
     }
 
@@ -171,4 +171,77 @@ public Long next() {
             }
         }
     }
+
+    public static Stream<Long> primeFactors(long target) {
+        return StreamSupport.stream(new PrimeFactorSpliterator(target), false);
+    }
+
+    private static class PrimeFactorSpliterator implements Spliterator<Long> {
+        private final PrimeFactorIterator primeFactorIterator;
+
+        PrimeFactorSpliterator(Long limit) {
+            primeFactorIterator = new PrimeFactorIterator(limit);
+        }
+
+        @Override
+        public boolean tryAdvance(Consumer<? super Long> action) {
+            if (primeFactorIterator.hasNext()) {
+                action.accept(primeFactorIterator.next());
+                return true;
+            }
+            return false;
+        }
+
+        @Override
+        public Spliterator<Long> trySplit() {
+            return null; // Sequential iteration only
+        }
+
+        @Override
+        public long estimateSize() {
+            return Long.MAX_VALUE; // Unknown size
+        }
+
+        @Override
+        public int characteristics() {
+            return ORDERED | SIZED | IMMUTABLE | NONNULL;
+        }
+    }
+
+    private static class PrimeFactorIterator implements Iterator<Long> {
+        private Long target;
+        private Long lastPrime;
+        private Iterator<Long> primeGenerator;
+
+        PrimeFactorIterator(Long target) {
+            this.target = target;
+            primeGenerator = new PrimeIterator(null);
+            lastPrime = primeGenerator.next();
+        }
+
+        @Override
+        public boolean hasNext() {
+            return this.target != 1;
+        }
+
+        @Override
+        public Long next() {
+            if (target < 0L) {
+                target = -target;
+                return -1L;
+            }
+            if (target == 0L) {
+                target = 1L;
+                return 0L;
+            }
+            while (hasNext()) {
+                while (target % lastPrime != 0L && lastPrime < target) {
+                    lastPrime = primeGenerator.next();
+                }
+                target /= lastPrime;
+                return lastPrime;
+            }
+            return null;
+        }
+    }
 }

java/src/main/java/euler/p0003.java

@@ -0,0 +1,25 @@
+/*
+Project Euler Problem 3
+
+The lesson I've taken from these is that Streams are significantly more cumbersome in Java than in other languages
+
+Problem:
+
+The prime factors of 13195 are 5, 7, 13 and 29.
+
+What is the largest prime factor of the number 600851475143 ?
+*/
+package euler;
+
+import java.util.Comparator;
+
+import euler.lib.Primes;
+
+public class p0003 implements IEuler {
+    @Override
+    public Object answer() {
+        return (short) Primes.primeFactors(600851475143L)
+                             .max(Comparator.naturalOrder())
+                             .get();
+    }
+}

java/src/test/java/EulerTest.java

@@ -17,6 +17,7 @@ static Stream<Object[]> data() throws IOException {
         return Stream.of(new Object[] { p0000.class, false, 0 },
                 new Object[] { p0001.class, false, Utilities.getAnswer(1) },
                 new Object[] { p0002.class, false, Utilities.getAnswer(2) },
+                new Object[] { p0003.class, false, Utilities.getAnswer(3) },
                 new Object[] { p0004.class, false, Utilities.getAnswer(4) },
                 new Object[] { p0006.class, false, Utilities.getAnswer(6) },
                 new Object[] { p0007.class, false, Utilities.getAnswer(7) },