func siftDownMin(h heap.Interface, i, n int) {
for (i*2+2)*2+2 < n { // has four grandchildren
m := minGrandchild(h, i, n)
if h.Less(i, m) {
return
}
h.Swap(i, m)
if h.Less(parent(m), m) {
h.Swap(m, parent(m))
}
i = m
}
if hasChild(i, n) {
m := minTwoGen(h, i, n)
if m > i*2+2 { // must be a grandchild
if h.Less(m, i) {
h.Swap(i, m)
if h.Less(parent(m), m) {
h.Swap(m, parent(m))
}
siftDownMin(h, m, n)
}
} else if h.Less(m, i) {
h.Swap(i, m)
}
}
}
// Iterative version after Bojesen, "Heap implementations and variations",
// http://www.diku.dk/forskning/performance-engineering/Jesper/heaplab/heapsurvey_html/node11.html
func siftDownMax(h heap.Interface, i, n int) {
for (i*2+2)*2+2 < n { // has four grandchildren
m := maxGrandchild(h, i, n)
if h.Less(m, i) {
return
}
h.Swap(i, m)
if h.Less(m, parent(m)) {
h.Swap(m, parent(m))
}
i = m
}
// XXX Following is from the original paper; couldn't get Bojesen's version
// to work.
if hasChild(i, n) {
m := maxTwoGen(h, i, n)
if m > i*2+2 { // must be a grandchild
if h.Less(i, m) {
h.Swap(i, m)
if h.Less(m, parent(m)) {
h.Swap(m, parent(m))
}
siftDownMax(h, m, n)
}
} else if h.Less(i, m) {
h.Swap(i, m)
}
}
}
func siftUpMin(h heap.Interface, i int) {
for gp := parent(parent(i)); gp >= 0; i, gp = gp, parent(parent(gp)) {
if h.Less(gp, i) {
break
}
h.Swap(i, gp)
}
}
func minGrandchild(h heap.Interface, i, n int) int {
cg := (i*2+1)*2 + 1
m := cg
for i := 1; i <= 3; i++ {
if h.Less(cg+i, m) {
m = cg + i
}
}
return m
}
// Index of minimum of children and grandchildren (if any) of i.
// Precondition: i has at least one child.
func minTwoGen(h heap.Interface, i, n int) int {
c1, c2 := i*2+1, i*2+2
m := c1
for _, k := range []int{c2, c1*2 + 1, c1*2 + 2, c2*2 + 1, c2*2 + 2} {
if k >= n {
break
}
if h.Less(k, m) {
m = k
}
}
return m
}
// Index of maximum element in h.
//
// There's no MinInd because the minimum of a heap is always at index zero.
func MaxInd(h heap.Interface) (maxind int) {
switch h.Len() {
case 1:
maxind = 0
case 2:
maxind = 1
default:
maxind = 1
if h.Less(1, 2) {
maxind = 2
}
}
return
}
// Removes and returns the maximum element of h.
func PopMax(h heap.Interface) interface{} {
n := h.Len()
if n <= 2 {
return h.Pop()
}
i := 1
if h.Less(1, 2) {
i = 2
}
h.Swap(i, n-1)
x := h.Pop()
siftDownMax(h, i, n-1)
return x
}
func siftUp(h heap.Interface, i int) {
if minLevel(i) {
if i > 0 && h.Less(parent(i), i) {
h.Swap(i, parent(i))
siftUpMax(h, parent(i))
} else {
siftUpMin(h, i)
}
} else {
if i > 0 && h.Less(i, parent(i)) {
h.Swap(i, parent(i))
siftUpMin(h, parent(i))
} else {
siftUpMax(h, i)
}
}
}