5 files changed, 157 insertions, 112 deletions

diff --git a/src/pkg/container/heap/example_intheap_test.go b/src/pkg/container/heap/example_intheap_test.go
new file mode 100644
index 000000000..e718cbc58
--- /dev/null
+++ b/src/pkg/container/heap/example_intheap_test.go
@@ -0,0 +1,43 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This example demonstrates an integer heap built using the heap interface.
+package heap_test
+
+import (
+	"container/heap"
+	"fmt"
+)
+
+// An IntHeap is a min-heap of ints.
+type IntHeap []int
+
+func (h IntHeap) Len() int           { return len(h) }
+func (h IntHeap) Less(i, j int) bool { return h[i] < h[j] }
+func (h IntHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }
+
+func (h *IntHeap) Push(x interface{}) {
+	// Push and Pop use pointer receivers because they modify the slice's length,
+	// not just its contents.
+	*h = append(*h, x.(int))
+}
+
+func (h *IntHeap) Pop() interface{} {
+	old := *h
+	n := len(old)
+	x := old[n-1]
+	*h = old[0 : n-1]
+	return x
+}
+
+// This example inserts several ints into an IntHeap and removes them in order of priority.
+func Example_intHeap() {
+	h := &IntHeap{2, 1, 5}
+	heap.Init(h)
+	heap.Push(h, 3)
+	for h.Len() > 0 {
+		fmt.Printf("%d ", heap.Pop(h))
+	}
+	// Output: 1 2 3 5
+}
diff --git a/src/pkg/container/heap/example_pq_test.go b/src/pkg/container/heap/example_pq_test.go
new file mode 100644
index 000000000..8cbeb8d70
--- /dev/null
+++ b/src/pkg/container/heap/example_pq_test.go
@@ -0,0 +1,95 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This example demonstrates a priority queue built using the heap interface.
+package heap_test
+
+import (
+	"container/heap"
+	"fmt"
+)
+
+// An Item is something we manage in a priority queue.
+type Item struct {
+	value    string // The value of the item; arbitrary.
+	priority int    // The priority of the item in the queue.
+	// The index is needed by update and is maintained by the heap.Interface methods.
+	index int // The index of the item in the heap.
+}
+
+// A PriorityQueue implements heap.Interface and holds Items.
+type PriorityQueue []*Item
+
+func (pq PriorityQueue) Len() int { return len(pq) }
+
+func (pq PriorityQueue) Less(i, j int) bool {
+	// We want Pop to give us the highest, not lowest, priority so we use greater than here.
+	return pq[i].priority > pq[j].priority
+}
+
+func (pq PriorityQueue) Swap(i, j int) {
+	pq[i], pq[j] = pq[j], pq[i]
+	pq[i].index = i
+	pq[j].index = j
+}
+
+func (pq *PriorityQueue) Push(x interface{}) {
+	n := len(*pq)
+	item := x.(*Item)
+	item.index = n
+	*pq = append(*pq, item)
+}
+
+func (pq *PriorityQueue) Pop() interface{} {
+	old := *pq
+	n := len(old)
+	item := old[n-1]
+	item.index = -1 // for safety
+	*pq = old[0 : n-1]
+	return item
+}
+
+// update modifies the priority and value of an Item in the queue.
+func (pq *PriorityQueue) update(item *Item, value string, priority int) {
+	heap.Remove(pq, item.index)
+	item.value = value
+	item.priority = priority
+	heap.Push(pq, item)
+}
+
+// This example inserts some items into a PriorityQueue, manipulates an item,
+// and then removes the items in priority order.
+func Example_priorityQueue() {
+	// Some items and their priorities.
+	items := map[string]int{
+		"banana": 3, "apple": 2, "pear": 4,
+	}
+
+	// Create a priority queue and put the items in it.
+	pq := &PriorityQueue{}
+	heap.Init(pq)
+	for value, priority := range items {
+		item := &Item{
+			value:    value,
+			priority: priority,
+		}
+		heap.Push(pq, item)
+	}
+
+	// Insert a new item and then modify its priority.
+	item := &Item{
+		value:    "orange",
+		priority: 1,
+	}
+	heap.Push(pq, item)
+	pq.update(item, item.value, 5)
+
+	// Take the items out; they arrive in decreasing priority order.
+	for pq.Len() > 0 {
+		item := heap.Pop(pq).(*Item)
+		fmt.Printf("%.2d:%s ", item.priority, item.value)
+	}
+	// Output:
+	// 05:orange 04:pear 03:banana 02:apple
+}
diff --git a/src/pkg/container/heap/example_test.go b/src/pkg/container/heap/example_test.go
deleted file mode 100644
index 2050bc835..000000000
--- a/src/pkg/container/heap/example_test.go
+++ /dev/null
@@ -1,105 +0,0 @@
-// Copyright 2012 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// This example demonstrates a priority queue built using the heap interface.
-package heap_test
-
-import (
-	"container/heap"
-	"fmt"
-)
-
-// An Item is something we manage in a priority queue.
-type Item struct {
-	value    string // The value of the item; arbitrary.
-	priority int    // The priority of the item in the queue.
-	// The index is needed by changePriority and is maintained by the heap.Interface methods.
-	index int // The index of the item in the heap.
-}
-
-// A PriorityQueue implements heap.Interface and holds Items.
-type PriorityQueue []*Item
-
-func (pq PriorityQueue) Len() int { return len(pq) }
-
-func (pq PriorityQueue) Less(i, j int) bool {
-	// We want Pop to give us the highest, not lowest, priority so we use greater than here.
-	return pq[i].priority > pq[j].priority
-}
-
-func (pq PriorityQueue) Swap(i, j int) {
-	pq[i], pq[j] = pq[j], pq[i]
-	pq[i].index = i
-	pq[j].index = j
-}
-
-func (pq *PriorityQueue) Push(x interface{}) {
-	// Push and Pop use pointer receivers because they modify the slice's length,
-	// not just its contents.
-	// To simplify indexing expressions in these methods, we save a copy of the
-	// slice object. We could instead write (*pq)[i].
-	a := *pq
-	n := len(a)
-	a = a[0 : n+1]
-	item := x.(*Item)
-	item.index = n
-	a[n] = item
-	*pq = a
-}
-
-func (pq *PriorityQueue) Pop() interface{} {
-	a := *pq
-	n := len(a)
-	item := a[n-1]
-	item.index = -1 // for safety
-	*pq = a[0 : n-1]
-	return item
-}
-
-// update is not used by the example but shows how to take the top item from
-// the queue, update its priority and value, and put it back.
-func (pq *PriorityQueue) update(value string, priority int) {
-	item := heap.Pop(pq).(*Item)
-	item.value = value
-	item.priority = priority
-	heap.Push(pq, item)
-}
-
-// changePriority is not used by the example but shows how to change the
-// priority of an arbitrary item.
-func (pq *PriorityQueue) changePriority(item *Item, priority int) {
-	heap.Remove(pq, item.index)
-	item.priority = priority
-	heap.Push(pq, item)
-}
-
-// This example pushes 10 items into a PriorityQueue and takes them out in
-// order of priority.
-func Example() {
-	const nItem = 10
-	// Random priorities for the items (a permutation of 0..9, times 11)).
-	priorities := [nItem]int{
-		77, 22, 44, 55, 11, 88, 33, 99, 00, 66,
-	}
-	values := [nItem]string{
-		"zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine",
-	}
-	// Create a priority queue and put some items in it.
-	pq := make(PriorityQueue, 0, nItem)
-	for i := 0; i < cap(pq); i++ {
-		item := &Item{
-			value:    values[i],
-			priority: priorities[i],
-		}
-		heap.Push(&pq, item)
-	}
-	// Take the items out; should arrive in decreasing priority order.
-	// For example, the highest priority (99) is the seventh item, so output starts with 99:"seven".
-	for i := 0; i < nItem; i++ {
-		item := heap.Pop(&pq).(*Item)
-		fmt.Printf("%.2d:%s ", item.priority, item.value)
-	}
-	// Output:
-	// 99:seven 88:five 77:zero 66:nine 55:three 44:two 33:six 22:one 11:four 00:eight
-}
diff --git a/src/pkg/container/heap/heap.go b/src/pkg/container/heap/heap.go
index 67018e6ba..c37e50e3c 100644
--- a/src/pkg/container/heap/heap.go
+++ b/src/pkg/container/heap/heap.go
@@ -4,13 +4,13 @@
 
 // Package heap provides heap operations for any type that implements
 // heap.Interface. A heap is a tree with the property that each node is the
-// highest-valued node in its subtree.
+// minimum-valued node in its subtree.
 //
 // A heap is a common way to implement a priority queue. To build a priority
 // queue, implement the Heap interface with the (negative) priority as the
 // ordering for the Less method, so Push adds items while Pop removes the
 // highest-priority item from the queue. The Examples include such an
-// implementation; the file example_test.go has the complete source.
+// implementation; the file example_pq_test.go has the complete source.
 //
 package heap
 
@@ -79,7 +79,7 @@ func Remove(h Interface, i int) interface{} {
 func up(h Interface, j int) {
 	for {
 		i := (j - 1) / 2 // parent
-		if i == j || h.Less(i, j) {
+		if i == j || !h.Less(j, i) {
 			break
 		}
 		h.Swap(i, j)
@@ -90,14 +90,14 @@ func up(h Interface, j int) {
 func down(h Interface, i, n int) {
 	for {
 		j1 := 2*i + 1
-		if j1 >= n {
+		if j1 >= n || j1 < 0 { // j1 < 0 after int overflow
 			break
 		}
 		j := j1 // left child
 		if j2 := j1 + 1; j2 < n && !h.Less(j1, j2) {
 			j = j2 // = 2*i + 2  // right child
 		}
-		if h.Less(i, j) {
+		if !h.Less(j, i) {
 			break
 		}
 		h.Swap(i, j)
diff --git a/src/pkg/container/heap/heap_test.go b/src/pkg/container/heap/heap_test.go
index cb31ef6d3..274d587d8 100644
--- a/src/pkg/container/heap/heap_test.go
+++ b/src/pkg/container/heap/heap_test.go
@@ -2,10 +2,9 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package heap_test
+package heap
 
 import (
-	. "container/heap"
 	"testing"
 )
 
@@ -170,3 +169,16 @@ func TestRemove2(t *testing.T) {
 		}
 	}
 }
+
+func BenchmarkDup(b *testing.B) {
+	const n = 10000
+	h := make(myHeap, n)
+	for i := 0; i < b.N; i++ {
+		for j := 0; j < n; j++ {
+			Push(&h, 0) // all elements are the same
+		}
+		for h.Len() > 0 {
+			Pop(&h)
+		}
+	}
+}