d18

day18/heap.swift

@@ -0,0 +1,54 @@
+struct Heap<T> {
+    var comparator: ((_ l: T,_ r: T) -> Bool)
+    var heap: [T] = []
+    var isEmpty: Bool { return heap.isEmpty }
+
+    private mutating func bubbleUp(idx: Int) {
+        let parent = (idx - 1) / 2
+        if idx <= 0 {
+            return
+        }
+        if comparator(heap[idx], heap[parent]) {
+            heap.swapAt(parent, idx)
+            bubbleUp(idx: parent)
+        }
+    }
+
+    private mutating func heapify(_ idx: Int) {
+        let left = idx * 2 + 1
+        let right = idx * 2 + 2
+        var comp = idx
+
+        if heap.count > left && comparator(heap[left], heap[comp]) {
+            comp = left
+        }
+        if heap.count > right && comparator(heap[right], heap[comp]) {
+            comp = right
+        }
+        if comp != idx {
+            heap.swapAt(comp, idx)
+            heapify(comp)
+        }
+    }
+
+    mutating func insert(_ item: T) {
+        heap.append(item)
+        bubbleUp(idx: heap.count-1)
+    }
+
+    mutating func pop() -> T? {
+        let item: T? = heap.first
+        if heap.count == 0 {
+            return nil
+        }
+        if heap.count > 1 {
+            heap[0] = heap[heap.count-1]
+            heap.removeLast()
+            heapify(0)
+        } else if heap.count == 1{
+            heap.removeLast()
+        }
+        return item
+    }
+}
+