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// 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.
// Copy of go/src/pkg/sort/sort.go, specialized for []int
// and to remove some array indexing.
package main
func min(a, b int) int {
if a < b {
return a
}
return b
}
// Insertion sort
func insertionSort(data []int, a, b int) {
for i := a + 1; i < b; i++ {
for j := i; j > a && data[j] < data[j-1]; j-- {
data[j], data[j-1] = data[j-1], data[j]
}
}
}
// siftDown implements the heap property on data[lo, hi).
// first is an offset into the array where the root of the heap lies.
func siftDown(data []int, lo, hi, first int) {
root := lo
for {
child := 2*root + 1
if child >= hi {
break
}
if child+1 < hi && data[first+child] < data[first+child+1] {
child++
}
if !(data[first+root] < data[first+child]) {
return
}
data[first+root], data[first+child] = data[first+child], data[first+root]
root = child
}
}
func heapSort(data []int, a, b int) {
first := a
lo := 0
hi := b - a
// Build heap with greatest element at top.
for i := (hi - 1) / 2; i >= 0; i-- {
siftDown(data, i, hi, first)
}
// Pop elements, largest first, into end of data.
for i := hi - 1; i >= 0; i-- {
data[first], data[first+i] = data[first+i], data[first]
siftDown(data, lo, i, first)
}
}
// Quicksort, following Bentley and McIlroy,
// ``Engineering a Sort Function,'' SP&E November 1993.
// medianOfThree moves the median of the three values data[a], data[b], data[c] into data[a].
func medianOfThree(data []int, a, b, c int) {
m0 := b
m1 := a
m2 := c
// bubble sort on 3 elements
if data[m1] < data[m0] {
data[m1], data[m0] = data[m0], data[m1]
}
if data[m2] < data[m1] {
data[m2], data[m1] = data[m1], data[m2]
}
if data[m1] < data[m0] {
data[m1], data[m0] = data[m0], data[m1]
}
// now data[m0] <= data[m1] <= data[m2]
}
func swapRange(data []int, a, b, n int) {
for i := 0; i < n; i++ {
data[a+i], data[b+i] = data[b+i], data[a+i]
}
}
func doPivot(data []int, lo, hi int) (midlo, midhi int) {
m := lo + (hi-lo)/2 // Written like this to avoid integer overflow.
if hi-lo > 40 {
// Tukey's ``Ninther,'' median of three medians of three.
s := (hi - lo) / 8
medianOfThree(data, lo, lo+s, lo+2*s)
medianOfThree(data, m, m-s, m+s)
medianOfThree(data, hi-1, hi-1-s, hi-1-2*s)
}
medianOfThree(data, lo, m, hi-1)
// Invariants are:
// data[lo] = pivot (set up by ChoosePivot)
// data[lo <= i < a] = pivot
// data[a <= i < b] < pivot
// data[b <= i < c] is unexamined
// data[c <= i < d] > pivot
// data[d <= i < hi] = pivot
//
// Once b meets c, can swap the "= pivot" sections
// into the middle of the slice.
pivot := lo
a, b, c, d := lo+1, lo+1, hi, hi
dpivot := data[pivot]
db, dc1 := data[b], data[c-1]
for b < c {
if db < dpivot { // data[b] < pivot
b++
if b < c {
db = data[b]
}
continue
}
if !(dpivot < db) { // data[b] = pivot
data[a], data[b] = db, data[a]
a++
b++
if b < c {
db = data[b]
}
continue
}
if dpivot < dc1 { // data[c-1] > pivot
c--
if c > 0 {
dc1 = data[c-1]
}
continue
}
if !(dc1 < dpivot) { // data[c-1] = pivot
data[c-1], data[d-1] = data[d-1], dc1
c--
d--
if c > 0 {
dc1 = data[c-1]
}
continue
}
// data[b] > pivot; data[c-1] < pivot
data[b], data[c-1] = dc1, db
b++
c--
if b < c {
db = data[b]
dc1 = data[c-1]
}
}
n := min(b-a, a-lo)
swapRange(data, lo, b-n, n)
n = min(hi-d, d-c)
swapRange(data, c, hi-n, n)
return lo + b - a, hi - (d - c)
}
func quickSort(data []int, a, b, maxDepth int) {
for b-a > 7 {
if maxDepth == 0 {
heapSort(data, a, b)
return
}
maxDepth--
mlo, mhi := doPivot(data, a, b)
// Avoiding recursion on the larger subproblem guarantees
// a stack depth of at most lg(b-a).
if mlo-a < b-mhi {
quickSort(data, a, mlo, maxDepth)
a = mhi // i.e., quickSort(data, mhi, b)
} else {
quickSort(data, mhi, b, maxDepth)
b = mlo // i.e., quickSort(data, a, mlo)
}
}
if b-a > 1 {
insertionSort(data, a, b)
}
}
func sortInts(data []int) {
// Switch to heapsort if depth of 2*ceil(lg(n)) is reached.
n := len(data)
maxDepth := 0
for 1<<uint(maxDepth) < n {
maxDepth++
}
maxDepth *= 2
quickSort(data, 0, n, maxDepth)
}
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