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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. // The sort package provides primitives for sorting arrays // and user-defined collections. package sort // SortInterface is the interface that a type, typically a collection, // must implement for its contents to be sorted in increasing order. // Its methods require that the elements of the collection be enumerated // by an integer index. type SortInterface interface { // Len is the number of elements in the collection. Len() int; // Less returns whether the element with index i is should sort // before the element with index j. // TODO(r): should this method be renamed Before? Less(i, j int) bool; // Swap swaps the elements with indexes i and j. 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 // IntArray attaches the methods of SortInterface to []int, sorting in increasing order. 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]; } // FloatArray attaches the methods of SortInterface to []float, sorting in increasing order. 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]; } // StringArray attaches the methods of SortInterface to []string, sorting in increasing order. 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 // SortInts sorts an array of ints in increasing order. func SortInts(a []int) { Sort(IntArray(a)); } // SortFloats sorts an array of floats in increasing order. func SortFloats(a []float) { Sort(FloatArray(a)); } // SortStrings sorts an array of strings in increasing order. func SortStrings(a []string) { Sort(StringArray(a)); } // IntsAreSorted tests whether an array of ints is sorted in increasing order. func IntsAreSorted(a []int) bool { return IsSorted(IntArray(a)); } // FloatsAreSorted tests whether an array of floats is sorted in increasing order. func FloatsAreSorted(a []float) bool { return IsSorted(FloatArray(a)); } // StringsAreSorted tests whether an array of strings is sorted in increasing order. func StringsAreSorted(a []string) bool { return IsSorted(StringArray(a)); }