feat: add MaxHeap

datastructure/heap/maxheap.go

@@ -0,0 +1,52 @@
+// Copyright 2021 dudaodong@gmail.com. All rights reserved.
+// Use of this source code is governed by MIT license
+
+// Package datastructure implements some data structure. eg. list, linklist, stack, queue, tree, graph.
+package datastructure
+
+import (
+	"github.com/duke-git/lancet/v2/lancetconstraints"
+)
+
+// MaxHeap implements a binary max heap
+// type T should implements Compare function in lancetconstraints.Comparator interface.
+type MaxHeap[T any] struct {
+	data       []T
+	comparator lancetconstraints.Comparator
+}
+
+// NewMaxHeap returns a MaxHeap instance with the given comparator.
+func NewMaxHeap[T any](comparator lancetconstraints.Comparator) *MaxHeap[T] {
+	return &MaxHeap[T]{
+		data:       make([]T, 0),
+		comparator: comparator,
+	}
+}
+
+// heapifyUp heapify the data from bottom to up
+func (h *MaxHeap[T]) heapifyUp(i int) {
+	for h.comparator.Compare(h.data[parentIndex(i)], h.data[i]) < 0 {
+		h.swap(parentIndex(i), i)
+		i = parentIndex(i)
+	}
+}
+
+// parentIndex get parent index of the given index
+func parentIndex(i int) int {
+	return (i - 1) / 2
+}
+
+// leftChildIndex get left child index of the given index
+func leftChildIndex(i int) int {
+	return 2*i + 1
+}
+
+// rightChildIndex get right child index of the given index
+func rightChildIndex(i int) int {
+	return 2*i + 2
+}
+
+// swap two elements in the heap
+func (h *MaxHeap[T]) swap(i, j int) {
+	h.data[i], h.data[j] = h.data[j], h.data[i]
+}