From 5d754e35efa5e13275b44196bdc6d539f7455120 Mon Sep 17 00:00:00 2001
From: ksw2000 <13825170+ksw2000@users.noreply.github.com>
Date: Wed, 17 Jul 2024 17:46:21 +0800
Subject: [PATCH] Reset heaps after union operation.

---
 heap.go      | 9 ++++++++-
 heap_test.go | 7 +++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/heap.go b/heap.go
index 2c76eaf..0e8fd23 100644
--- a/heap.go
+++ b/heap.go
@@ -267,7 +267,8 @@ func (h *Heap[K, V]) cascadingCut(y *Element[K, V]) {
 }
 
 // Union unions the two fibonacci heaps h and g, and returns the new fibonacci
-// heap with amortized running time Θ(1).
+// heap with amortized running time Θ(1). The heap h and g will be reset after
+// unioning.
 func (h *Heap[K, V]) Union(g *Heap[K, V]) *Heap[K, V] {
 	if h == nil || g == nil {
 		panic("fibheap: Union expects non-nil heap h and g")
@@ -295,5 +296,11 @@ func (h *Heap[K, V]) Union(g *Heap[K, V]) *Heap[K, V] {
 		m.min = g.min
 	}
 
+	// clear heap h and heap g
+	h.min = nil
+	h.elements = 0
+	g.min = nil
+	g.elements = 0
+
 	return m
 }
diff --git a/heap_test.go b/heap_test.go
index 30f07be..aca1ea0 100644
--- a/heap_test.go
+++ b/heap_test.go
@@ -89,4 +89,11 @@ func TestUnion(t *testing.T) {
 		x := k.ExtractMin()
 		assert(t, x.Key(), i)
 	}
+
+	if h.min != nil || h.elements != 0 {
+		t.Fatal("h should be clear after Union")
+	}
+	if g.min != nil || g.elements != 0 {
+		t.Fatal("g should be clear after Union")
+	}
 }