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/* | |
Package minheap provides an implementation of a Min Heap data structure | |
*/ | |
package minheap | |
import ( | |
"log" | |
"github.com/dorin131/go-data-structures/heap" | |
) | |
// MinHeap : represents a Min Heap data structure | |
type MinHeap struct { | |
*heap.Heap | |
} | |
// New : returns a new instance of a Heap | |
func New(input []int) *MinHeap { | |
h := &MinHeap{ | |
&heap.Heap{ | |
Items: input, | |
}, | |
} | |
if len(h.Items) > 0 { | |
h.buildMinHeap() | |
} | |
return h | |
} | |
// ExtractMin : removes top element of the heap and returns it | |
func (h *MinHeap) ExtractMin() int { | |
if len(h.Items) == 0 { | |
log.Fatal("No items in the heap") | |
} | |
minItem := h.Items[0] | |
lastIndex := len(h.Items) - 1 | |
h.Items[0] = h.Items[lastIndex] | |
// shrinking slice | |
h.Items = h.Items[:len(h.Items)-1] | |
h.minHeapifyDown(0) | |
return minItem | |
} | |
// Insert : adds a new element to the heap | |
func (h *MinHeap) Insert(item int) *MinHeap { | |
h.Items = append(h.Items, item) | |
lastElementIndex := len(h.Items) - 1 | |
h.minHeapifyUp(lastElementIndex) | |
return h | |
} | |
// buildMinHeap : given a slice, arrange the elements so that | |
// they satisfy the Min Heap properties | |
func (h *MinHeap) buildMinHeap() { | |
for i := len(h.Items)/2 - 1; i >= 0; i-- { | |
h.minHeapifyDown(i) | |
} | |
} | |
// minHeapifyDown : takes the top element and moves it down until | |
// the Min Heap properties are satisfied | |
func (h *MinHeap) minHeapifyDown(index int) { | |
for (h.HasLeft(index) && (h.Items[index] > h.Left(index))) || | |
(h.HasRight(index) && (h.Items[index] > h.Right(index))) { | |
if (h.HasLeft(index) && (h.Items[index] > h.Left(index))) && | |
(h.HasRight(index) && (h.Items[index] > h.Right(index))) { | |
if h.Left(index) < h.Right(index) { | |
h.Swap(index, h.GetLeftIndex(index)) | |
index = h.GetLeftIndex(index) | |
} else { | |
h.Swap(index, h.GetRightIndex(index)) | |
index = h.GetRightIndex(index) | |
} | |
} else if h.HasLeft(index) && (h.Items[index] > h.Left(index)) { | |
h.Swap(index, h.GetLeftIndex(index)) | |
index = h.GetLeftIndex(index) | |
} else { | |
h.Swap(index, h.GetRightIndex(index)) | |
index = h.GetRightIndex(index) | |
} | |
} | |
} | |
// minHeapUp : takes the last element and moves it up until | |
// the Min Heap properties are satisfied | |
func (h *MinHeap) minHeapifyUp(index int) { | |
for h.HasParent(index) && (h.Parent(index) > h.Items[index]) { | |
h.Swap(h.GetParentIndex(index), index) | |
index = h.GetParentIndex(index) | |
} | |
} |