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// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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2009-03-06 18:29:25 -07:00
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// The sort package provides primitives for sorting arrays
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// and user-defined collections.
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package sort
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// SortInterface is the interface that a type, typically a collection,
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// must implement for its contents to be sorted in increasing order.
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// Its methods require that the elements of the collection be enumerated
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// by an integer index.
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type SortInterface interface {
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// Len is the number of elements in the collection.
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Len() int;
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// Less returns whether the element with index i is should sort
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// before the element with index j.
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// TODO(r): should this method be renamed Before?
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Less(i, j int) bool;
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// Swap swaps the elements with indexes i and j.
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Swap(i, j int);
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}
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func min(a, b int) int {
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if a < b {
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return a;
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}
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return b;
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}
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// Insertion sort
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func insertionSort(data SortInterface, a, b int) {
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for i := a+1; i < b; i++ {
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for j := i; j > a && data.Less(j, j-1); j-- {
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data.Swap(j, j-1);
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}
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}
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}
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// Quicksort, following Bentley and McIlroy,
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// ``Engineering a Sort Function,'' SP&E November 1993.
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// Move the median of the three values data[a], data[b], data[c] into data[a].
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func medianOfThree(data SortInterface, a, b, c int) {
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m0 := b;
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m1 := a;
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m2 := c;
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// bubble sort on 3 elements
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if data.Less(m1, m0) { data.Swap(m1, m0); }
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if data.Less(m2, m1) { data.Swap(m2, m1); }
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if data.Less(m1, m0) { data.Swap(m1, m0); }
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// now data[m0] <= data[m1] <= data[m2]
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}
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func swapRange(data SortInterface, a, b, n int) {
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for i := 0; i < n; i++ {
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data.Swap(a+i, b+i);
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}
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}
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func doPivot(data SortInterface, lo, hi int) (midlo, midhi int) {
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m := (lo+hi)/2;
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if hi - lo > 40 {
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// Tukey's ``Ninther,'' median of three medians of three.
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s := (hi - lo) / 8;
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medianOfThree(data, lo, lo+s, lo+2*s);
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medianOfThree(data, m, m-s, m+s);
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medianOfThree(data, hi-1, hi-1-s, hi-1-2*s);
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}
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medianOfThree(data, lo, m, hi-1);
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// Invariants are:
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// data[lo] = pivot (set up by ChoosePivot)
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// data[lo <= i < a] = pivot
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// data[a <= i < b] < pivot
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// data[b <= i < c] is unexamined
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// data[c <= i < d] > pivot
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// data[d <= i < hi] = pivot
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//
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// Once b meets c, can swap the "= pivot" sections
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// into the middle of the array.
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pivot := lo;
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a, b, c, d := lo+1, lo+1, hi, hi;
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for b < c {
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if data.Less(b, pivot) { // data[b] < pivot
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b++;
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continue;
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}
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if !data.Less(pivot, b) { // data[b] = pivot
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data.Swap(a, b);
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a++;
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b++;
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continue;
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}
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if data.Less(pivot, c-1) { // data[c-1] > pivot
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c--;
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continue;
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}
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if !data.Less(c-1, pivot) { // data[c-1] = pivot
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data.Swap(c-1, d-1);
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c--;
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d--;
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continue;
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}
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// data[b] > pivot; data[c-1] < pivot
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data.Swap(b, c-1);
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b++;
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c--;
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}
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n := min(b-a, a-lo);
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swapRange(data, lo, b-n, n);
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n = min(hi-d, d-c);
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swapRange(data, c, hi-n, n);
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return lo+b-a, hi-(d-c);
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}
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func quickSort(data SortInterface, a, b int) {
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if b - a > 7 {
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mlo, mhi := doPivot(data, a, b);
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quickSort(data, a, mlo);
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quickSort(data, mhi, b);
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} else if b - a > 1 {
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insertionSort(data, a, b);
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}
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}
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func Sort(data SortInterface) {
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quickSort(data, 0, data.Len());
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}
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func IsSorted(data SortInterface) bool {
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n := data.Len();
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for i := n - 1; i > 0; i-- {
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if data.Less(i, i - 1) {
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return false;
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}
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}
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return true;
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}
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// Convenience types for common cases
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// IntArray attaches the methods of SortInterface to []int, sorting in increasing order.
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type IntArray []int
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func (p IntArray) Len() int { return len(p); }
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func (p IntArray) Less(i, j int) bool { return p[i] < p[j]; }
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func (p IntArray) Swap(i, j int) { p[i], p[j] = p[j], p[i]; }
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// FloatArray attaches the methods of SortInterface to []float, sorting in increasing order.
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type FloatArray []float
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func (p FloatArray) Len() int { return len(p); }
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func (p FloatArray) Less(i, j int) bool { return p[i] < p[j]; }
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func (p FloatArray) Swap(i, j int) { p[i], p[j] = p[j], p[i]; }
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// StringArray attaches the methods of SortInterface to []string, sorting in increasing order.
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type StringArray []string
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func (p StringArray) Len() int { return len(p); }
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func (p StringArray) Less(i, j int) bool { return p[i] < p[j]; }
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func (p StringArray) Swap(i, j int) { p[i], p[j] = p[j], p[i]; }
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// Convenience wrappers for common cases
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// SortInts sorts an array of ints in increasing order.
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func SortInts(a []int) { Sort(IntArray(a)); }
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// SortFloats sorts an array of floats in increasing order.
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func SortFloats(a []float) { Sort(FloatArray(a)); }
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// SortStrings sorts an array of strings in increasing order.
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func SortStrings(a []string) { Sort(StringArray(a)); }
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// IntsAreSorted tests whether an array of ints is sorted in increasing order.
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func IntsAreSorted(a []int) bool { return IsSorted(IntArray(a)); }
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// FloatsAreSorted tests whether an array of floats is sorted in increasing order.
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func FloatsAreSorted(a []float) bool { return IsSorted(FloatArray(a)); }
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// StringsAreSorted tests whether an array of strings is sorted in increasing order.
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func StringsAreSorted(a []string) bool { return IsSorted(StringArray(a)); }
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