5kyu: add „Product of consecutive Fib numbers“

Signed-off-by: Matej Focko <mfocko@redhat.com>

5kyu/product_of_consecutive_fib_numbers/solution.kt

@@ -0,0 +1,61 @@
+package prodfib
+
+class FibonacciPairs : Iterable<Pair<Long, Long>> {
+    private class FibonacciPairsIterator : Iterator<Pair<Long, Long>> {
+        private var a: Long = 0
+        private var b: Long = 1
+
+        /**
+         * Returns `true` if the iteration has more elements.
+         */
+        override fun hasNext(): Boolean = true
+
+        /**
+         * Returns the next element in the iteration.
+         */
+        override fun next(): Pair<Long, Long> {
+            val current = a to b
+
+            a = current.second
+            b = current.first + current.second
+
+            return current
+        }
+    }
+
+    /**
+     * Returns an iterator over the elements of this object.
+     */
+    override fun iterator(): Iterator<Pair<Long, Long>> = FibonacciPairsIterator()
+}
+
+fun productFib(prod: Long): LongArray =
+    FibonacciPairs()
+        .asSequence()
+        .dropWhile { (a, b) -> a * b < prod }
+        .first()
+        .let { (a, b) ->
+            longArrayOf(
+                a, b, if (a * b == prod) {
+                    1
+                } else {
+                    0
+                }
+            )
+        }
+
+fun main() {
+    (0 until 10).zip(FibonacciPairs()).forEach { (i, pair) ->
+        println("$i → $pair")
+    }
+
+    val tests = mapOf(
+        4895L to longArrayOf(55, 89, 1),
+        5895L to longArrayOf(89, 144, 0),
+        714L to longArrayOf(21, 34, 1),
+        800L to longArrayOf(34, 55, 0),
+    )
+    tests.forEach { (prod, expected) ->
+        check(productFib(prod).contentEquals(expected))
+    }
+}

README.md

@@ -66,6 +66,7 @@
 - [Buddy Pairs](https://www.codewars.com/kata/59ccf051dcc4050f7800008f) - [solution](5kyu/buddy_pairs)
 - [Simple assembler interpreter](https://www.codewars.com/kata/58e24788e24ddee28e000053) - [solution](5kyu/simple_assembler_interpreter)
 - [Maximum subarray sum](https://www.codewars.com/kata/54521e9ec8e60bc4de000d6c) - [solution](5kyu/maximum_subarray_sum)
+- [Product of consecutive Fib numbers](https://www.codewars.com/kata/5541f58a944b85ce6d00006a) - [solution](5kyu/product_of_consecutive_fib_numbers)
 
 ### C#