fix bug

fix pullDown

src/main/kotlin/it/norangeb/algorithms/datastructures/queue/priority/BinaryHeap.kt

@@ -30,7 +30,7 @@ import arrow.core.Option
 import arrow.core.toOption
 
 class BinaryHeap<T> private constructor(
-    private var array: Array<T?>,
+    var array: Array<T?>,
     private val shouldExchange: (T, T) -> Boolean
 ) : PriorityQueue<T> {
     private var size: Int = 0
@@ -80,23 +80,23 @@ class BinaryHeap<T> private constructor(
     }
 
     private fun pullDown(array: Array<T?>, k: Int) {
-        var i = k
-        while (i * WAY <= size) {
-            val child = i * WAY
-
-            when {
-                array[child + 1] == null -> exchange(array, i, child)
+        var i = k * WAY
+        while (i <= size) {
+            val child = when {
+                array[i + 1] == null -> i
                 shouldExchange(
-                    array[child] ?: return,
-                    array[child + 1] ?: return
-                ) -> exchange(array, i, child + 1)
-                else -> exchange(array, i, child)
+                    array[i] ?: return,
+                    array[i + 1] ?: return
+                ) -> i + 1
+                else -> i
             }
 
-            i *= WAY
+            exchange(array, child / 2, child)
+
+            i = 2 * child
         }
 
-        pushUp(array, i)
+        pushUp(array, i / 2)
     }
 
     private fun exchange(array: Array<T?>, i: Int, j: Int) {

src/test/kotlin/it/norangeb/algorithms/datastructures/queue/priority/BinaryHeapTest.kt

@@ -64,6 +64,64 @@ class BinaryHeapTest {
         array `should equal` arrayOf(Int.MAX_VALUE, 23, 7, 12, 3, 5)
     }
 
+    @Test
+    fun testMinQueue() {
+        val heap = BinaryHeap.createMinPriorityQueue<Double>()
+
+        heap.insert(0.37)
+
+        heap.peek().map { it `should be equal to` 0.37 }
+
+        heap.insert(0.19)
+
+        heap.peek().map { it `should be equal to` 0.19 }
+
+        heap.insert(0.34)
+
+        heap.peek().map { it `should be equal to` 0.19 }
+
+        heap.insert(0.26)
+
+        heap.peek().map { it `should be equal to` 0.19 }
+
+        heap.insert(0.16)
+
+        heap.peek().map { it `should be equal to` 0.16 }
+
+        heap.insert(0.40)
+
+        heap.peek().map { it `should be equal to` 0.16 }
+
+        heap.insert(0.28)
+
+        heap.peek().map { it `should be equal to` 0.16 }
+
+        heap.insert(0.38)
+        heap.insert(0.17)
+        heap.insert(0.29)
+        heap.insert(0.32)
+        heap.insert(0.35)
+        heap.insert(0.36)
+        heap.insert(0.52)
+
+        heap.peek().map { it `should be equal to` 0.16 }
+        heap.pop().map { it `should be equal to` 0.16 }
+        heap.pop().map { it `should be equal to` 0.17 }
+        heap.pop().map { it `should be equal to` 0.19 }
+        heap.pop().map { it `should be equal to` 0.26 }
+        heap.pop().map { it `should be equal to` 0.28 }
+        heap.pop().map { it `should be equal to` 0.29 }
+        heap.pop().map { it `should be equal to` 0.32 }
+        heap.pop().map { it `should be equal to` 0.34 }
+        heap.pop().map { it `should be equal to` 0.35 }
+        heap.pop().map { it `should be equal to` 0.36 }
+        heap.pop().map { it `should be equal to` 0.37 }
+        heap.pop().map { it `should be equal to` 0.38 }
+        heap.pop().map { it `should be equal to` 0.40 }
+        heap.pop().map { it `should be equal to` 0.52 }
+        heap.pop() `should equal` None
+    }
+
     @Test
     fun testComparableMax() {
         val heap = BinaryHeap.createMaxPriorityQueue<Int>()