changed subtraction to modulo division for euclid algo, create a new factorial function with Kotlin optimization (tailrec), changed calculating middle variable in binary search

src/main/kotlin/other/Euclid.kt

@@ -15,14 +15,14 @@ class Euclid {
     fun compute(num1: Int, num2: Int) : Int {
         var copyNum1 = num1
         var copyNum2 = num2
-        while (copyNum1 != copyNum2) {
+        while (copyNum1 != 0 && copyNum2 != 0) {
             if (copyNum1 > copyNum2) {
-                copyNum1 -= copyNum2
+                copyNum1 %= copyNum2
             } else {
-                copyNum2 -= copyNum1
+                copyNum2 %= copyNum1
             }
         }
-        return copyNum1
+        return copyNum1 + copyNum2
     }
 
 }

src/main/kotlin/other/Factorial.kt

@@ -39,4 +39,11 @@ class Factorial {
         }
     }
 
+    /**
+     * @see <a href="https://kotlinlang.org/docs/functions.html#tail-recursive-functions">tailrec functions</a>
+     *
+     */
+    tailrec fun computeRecursiveWithKotlinOptimization(number: Int) : Int =
+        if (number <= 1) 1 else number * computeRecursiveWithKotlinOptimization(number - 1)
+
 }

src/main/kotlin/search/BinarySearch.kt

@@ -22,7 +22,7 @@ class BinarySearch<T : Comparable<T>> : Search<T> {
         var left = -1
         var right = array.size
         while ((right - left) > 1) {
-            val middle = (right + left) / 2
+            val middle = left + (right - left) / 2
             if (element > array[middle]) {
                 left = middle
             } else {

src/test/kotlin/other/FactorialTest.kt

@@ -25,6 +25,14 @@ internal class FactorialTest {
         assertEquals(720, factorial.computeRecursive(6))
     }
 
+    @Test
+    fun test_recursive_with_kotlin_optimization() {
+        assertEquals(1, factorial.computeRecursiveWithKotlinOptimization(0))
+        assertEquals(1, factorial.computeRecursiveWithKotlinOptimization(1))
+        assertEquals(6, factorial.computeRecursiveWithKotlinOptimization(3))
+        assertEquals(120, factorial.computeRecursiveWithKotlinOptimization(5))
+        assertEquals(720, factorial.computeRecursiveWithKotlinOptimization(6))
+    }
 
 
 }