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// Copyright 2009 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.
package sort
type SortInterface interface {
Len() int;
Less(i, j int) bool;
Swap(i, j int);
}
func min(a, b int) int {
if a < b {
return a;
}
return b;
}
// Insertion sort
func insertionSort(data SortInterface, a, b int) {
for i := a+1; i < b; i++ {
for j := i; j > a && data.Less(j, j-1); j-- {
data.Swap(j, j-1);
}
}
}
// Quicksort, following Bentley and McIlroy,
// ``Engineering a Sort Function,'' SP&E November 1993.
// Move the median of the three values data[a], data[b], data[c] into data[a].
func medianOfThree(data SortInterface, a, b, c int) {
m0 := b;
m1 := a;
m2 := c;
// bubble sort on 3 elements
if data.Less(m1, m0) { data.Swap(m1, m0); }
if data.Less(m2, m1) { data.Swap(m2, m1); }
if data.Less(m1, m0) { data.Swap(m1, m0); }
// now data[m0] <= data[m1] <= data[m2]
}
func swapRange(data SortInterface, a, b, n int) {
for i := 0; i < n; i++ {
data.Swap(a+i, b+i);
}
}
func doPivot(data SortInterface, lo, hi int) (midlo, midhi int) {
m := (lo+hi)/2;
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 array.
pivot := lo;
a, b, c, d := lo+1, lo+1, hi, hi;
for b < c {
if data.Less(b, pivot) { // data[b] < pivot
b++;
continue;
}
if !data.Less(pivot, b) { // data[b] = pivot
data.Swap(a, b);
a++;
b++;
continue;
}
if data.Less(pivot, c-1) { // data[c-1] > pivot
c--;
continue;
}
if !data.Less(c-1, pivot) { // data[c-1] = pivot
data.Swap(c-1, d-1);
c--;
d--;
continue;
}
// data[b] > pivot; data[c-1] < pivot
data.Swap(b, c-1);
b++;
c--;
}
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 SortInterface, a, b int) {
if b - a > 7 {
mlo, mhi := doPivot(data, a, b);
quickSort(data, a, mlo);
quickSort(data, mhi, b);
} else if b - a > 1 {
insertionSort(data, a, b);
}
}
func Sort(data SortInterface) {
quickSort(data, 0, data.Len());
}
func IsSorted(data SortInterface) bool {
n := data.Len();
for i := n - 1; i > 0; i-- {
if data.Less(i, i - 1) {
return false;
}
}
return true;
}
// Convenience types for common cases
type IntArray []int
func (p IntArray) Len() int { return len(p); }
func (p IntArray) Less(i, j int) bool { return p[i] < p[j]; }
func (p IntArray) Swap(i, j int) { p[i], p[j] = p[j], p[i]; }
type FloatArray []float
func (p FloatArray) Len() int { return len(p); }
func (p FloatArray) Less(i, j int) bool { return p[i] < p[j]; }
func (p FloatArray) Swap(i, j int) { p[i], p[j] = p[j], p[i]; }
type StringArray []string
func (p StringArray) Len() int { return len(p); }
func (p StringArray) Less(i, j int) bool { return p[i] < p[j]; }
func (p StringArray) Swap(i, j int) { p[i], p[j] = p[j], p[i]; }
// Convenience wrappers for common cases
func SortInts(a []int) { Sort(IntArray(a)); }
func SortFloats(a []float) { Sort(FloatArray(a)); }
func SortStrings(a []string) { Sort(StringArray(a)); }
func IntsAreSorted(a []int) bool { return IsSorted(IntArray(a)); }
func FloatsAreSorted(a []float) bool { return IsSorted(FloatArray(a)); }
func StringsAreSorted(a []string) bool { return IsSorted(StringArray(a)); }
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