github.com/chenjiandongx/go-queue@v0.0.0-20191023082232-e2a36f382f84/std_sort.go (about)

     1  package collections
     2  
     3  // Copyright 2009 The Go Authors. All rights reserved.
     4  // Use of this source code is governed by a BSD-style
     5  // license that can be found in the LICENSE file.
     6  
     7  //go:generate go run genzfunc.go
     8  
     9  // Package sort provides primitives for sorting slices and user-defined
    10  // collections.
    11  
    12  // Insertion sort
    13  func insertionSort(data []int, a, b int) {
    14  	for i := a + 1; i < b; i++ {
    15  		for j := i; j > a && data[j] < data[j-1]; j-- {
    16  			data[j], data[j-1] = data[j-1], data[j]
    17  		}
    18  	}
    19  }
    20  
    21  // siftDown implements the heap property on data[lo, hi).
    22  // first is an offset into the array where the root of the heap lies.
    23  func siftDown(data []int, lo, hi, first int) {
    24  	root := lo
    25  	for {
    26  		child := 2*root + 1
    27  		if child >= hi {
    28  			break
    29  		}
    30  		if child+1 < hi && data[first+child] < data[first+child+1] {
    31  			child++
    32  		}
    33  		if !(data[first+root] < data[first+child]) {
    34  			return
    35  		}
    36  		data[first+root], data[first+child] = data[first+child], data[first+root]
    37  		root = child
    38  	}
    39  }
    40  
    41  func heapSort(data []int, a, b int) {
    42  	first := a
    43  	lo := 0
    44  	hi := b - a
    45  
    46  	// Build heap with greatest element at top.
    47  	for i := (hi - 1) / 2; i >= 0; i-- {
    48  		siftDown(data, i, hi, first)
    49  	}
    50  
    51  	// Pop elements, largest first, into end of data.
    52  	for i := hi - 1; i >= 0; i-- {
    53  		data[first], data[first+i] = data[first+i], data[first]
    54  		siftDown(data, lo, i, first)
    55  	}
    56  }
    57  
    58  // Quicksort, loosely following Bentley and McIlroy,
    59  // ``Engineering a Sort Function,'' SP&E November 1993.
    60  
    61  // medianOfThree moves the median of the three values data[m0], data[m1], data[m2] into data[m1].
    62  func medianOfThree(data []int, m1, m0, m2 int) {
    63  	// sort 3 elements
    64  	if data[m1] < data[m0] {
    65  		data[m1], data[m0] = data[m0], data[m1]
    66  	}
    67  	// data[m0] <= data[m1]
    68  	if data[m2] < data[m1] {
    69  		data[m2], data[m1] = data[m1], data[m2]
    70  		if data[m1] < data[m0] {
    71  			data[m1], data[m0] = data[m0], data[m1]
    72  		}
    73  	}
    74  	// now data[m0] <= data[m1] <= data[m2]
    75  }
    76  
    77  func doPivot(data []int, lo, hi int) (midlo, midhi int) {
    78  	m := int(uint(lo+hi) >> 1) // Written like this to avoid integer overflow.
    79  	if hi-lo > 40 {
    80  		// Tukey's ``Ninther,'' median of three medians of three.
    81  		s := (hi - lo) / 8
    82  		medianOfThree(data, lo, lo+s, lo+2*s)
    83  		medianOfThree(data, m, m-s, m+s)
    84  		medianOfThree(data, hi-1, hi-1-s, hi-1-2*s)
    85  	}
    86  	medianOfThree(data, lo, m, hi-1)
    87  
    88  	// Invariants are:
    89  	//	data[lo] = pivot (set up by ChoosePivot)
    90  	//	data[lo < i < a] < pivot
    91  	//	data[a <= i < b] <= pivot
    92  	//	data[b <= i < c] unexamined
    93  	//	data[c <= i < hi-1] > pivot
    94  	//	data[hi-1] >= pivot
    95  	pivot := lo
    96  	a, c := lo+1, hi-1
    97  
    98  	for ; a < c && data[a] < data[pivot]; a++ {
    99  	}
   100  	b := a
   101  	for {
   102  		for ; b < c && !(data[pivot] < data[b]); b++ { // data[b] <= pivot
   103  		}
   104  		for ; b < c && data[pivot] < data[c-1]; c-- { // data[c-1] > pivot
   105  		}
   106  		if b >= c {
   107  			break
   108  		}
   109  		// data[b] > pivot; data[c-1] <= pivot
   110  		data[b], data[c-1] = data[c-1], data[b]
   111  		b++
   112  		c--
   113  	}
   114  	// If hi-c<3 then there are duplicates (by property of median of nine).
   115  	// Let be a bit more conservative, and set border to 5.
   116  	protect := hi-c < 5
   117  	if !protect && hi-c < (hi-lo)/4 {
   118  		// Lets test some points for equality to pivot
   119  		dups := 0
   120  		if !(data[pivot] < data[hi-1]) { // data[hi-1] = pivot
   121  			data[c], data[hi-1] = data[hi-1], data[c]
   122  			c++
   123  			dups++
   124  		}
   125  		if !(data[b-1] < data[pivot]) { // data[b-1] = pivot
   126  			b--
   127  			dups++
   128  		}
   129  		// m-lo = (hi-lo)/2 > 6
   130  		// b-lo > (hi-lo)*3/4-1 > 8
   131  		// ==> m < b ==> data[m] <= pivot
   132  		if !(data[m] < data[pivot]) { // data[m] = pivot
   133  			data[m], data[b-1] = data[b-1], data[m]
   134  			b--
   135  			dups++
   136  		}
   137  		// if at least 2 points are equal to pivot, assume skewed distribution
   138  		protect = dups > 1
   139  	}
   140  	if protect {
   141  		// Protect against a lot of duplicates
   142  		// Add invariant:
   143  		//	data[a <= i < b] unexamined
   144  		//	data[b <= i < c] = pivot
   145  		for {
   146  			for ; a < b && !(data[b-1] < data[pivot]); b-- { // data[b] == pivot
   147  			}
   148  			for ; a < b && data[a] < data[pivot]; a++ { // data[a] < pivot
   149  			}
   150  			if a >= b {
   151  				break
   152  			}
   153  			// data[a] == pivot; data[b-1] < pivot
   154  			data[a], data[b-1] = data[b-1], data[a]
   155  			a++
   156  			b--
   157  		}
   158  	}
   159  	// Swap pivot into middle
   160  	data[pivot], data[b-1] = data[b-1], data[pivot]
   161  	return b - 1, c
   162  }
   163  
   164  func qSort(data []int, a, b, maxDepth int) {
   165  	for b-a > 12 { // Use ShellSort for slices <= 12 elements
   166  		if maxDepth == 0 {
   167  			heapSort(data, a, b)
   168  			return
   169  		}
   170  		maxDepth--
   171  		mlo, mhi := doPivot(data, a, b)
   172  		// Avoiding recursion on the larger subproblem guarantees
   173  		// a stack depth of at most lg(b-a).
   174  		if mlo-a < b-mhi {
   175  			qSort(data, a, mlo, maxDepth)
   176  			a = mhi // i.e., quickSort(data, mhi, b)
   177  		} else {
   178  			qSort(data, mhi, b, maxDepth)
   179  			b = mlo // i.e., quickSort(data, a, mlo)
   180  		}
   181  	}
   182  	if b-a > 1 {
   183  		// Do ShellSort pass with gap 6
   184  		// It could be written in this simplified form cause b-a <= 12
   185  		for i := a + 6; i < b; i++ {
   186  			if data[i] < data[i-6] {
   187  				data[i], data[i-6] = data[i-6], data[i]
   188  			}
   189  		}
   190  		insertionSort(data, a, b)
   191  	}
   192  }
   193  
   194  // Sort sorts data.
   195  // It makes one call to data.Len to determine n, and O(n*log(n)) calls to
   196  // data.Less and data.Swap. The sort is not guaranteed to be stable.
   197  func stdSort(data []int, start, end int, ch chan bool) {
   198  	n := len(data)
   199  	mid := n / 2
   200  	qSort(data, start, end, maxDepth(mid))
   201  	ch <- true
   202  }
   203  
   204  func StdSortWithoutInterface(data []int) {
   205  	n := len(data)
   206  	mid := n / 2
   207  	qSort(data, 0, n, maxDepth(mid))
   208  }
   209  
   210  func maxDepth(n int) int {
   211  	var depth int
   212  	for i := n; i > 0; i >>= 1 {
   213  		depth++
   214  	}
   215  	return depth * 2
   216  }
   217  
   218  func StdSortWithGoroutine(data []int) {
   219  	n := len(data)
   220  	mid := n / 2
   221  
   222  	chs := make(chan bool, 2)
   223  
   224  	go stdSort(data, 0, mid, chs)
   225  	go stdSort(data, mid, n, chs)
   226  
   227  	for i := 0; i < 2; i++ {
   228  		<-chs
   229  	}
   230  	res := make([]int, n)
   231  	mergeArray(data, 0, mid-1, n-1, res)
   232  }