Gnome Sort
Gnome sort (Stupid sort), originally proposed by Hamid
Sarbazi-Azad in 2000 and called Stupid
sort (not to be confused with Bogosort), and then later on described by Dick Grune and named "Gnome
sort",[1] is a sorting algorithm which is similar to insertion sort, except that moving an element to
its proper place is accomplished by a series of swaps, as in bubble sort. It is conceptually simple,
requiring no nested loops. The running time is O , but tends towards O(n) if the
list is initially almost sorted.[2] In practice the algorithm can run
as fast asInsertion sort[citation
needed]. The average runtime is .
The algorithm always
finds the first place where two adjacent elements are in the wrong order, and
swaps them. It takes advantage of the fact that performing a swap can introduce
a new out-of-order adjacent pair only right before or after the two swapped
elements. It does not assume that elements forward of the current position are
sorted, so it only needs to check the position directly before the swapped
elements.
Class
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Data structure
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auxiliary
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Example
Given an unsorted array, a = [5, 3, 2, 4], the gnome sort would
take the following steps during the while loop. The "current
position" is highlighted in bold:
Current array
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Action to take
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[5, 3, 2, 4]
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a[pos] < a[pos-1], swap:
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[3, 5, 2, 4]
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a[pos] >= a[pos-1], increment pos:
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[3, 5, 2, 4]
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a[pos] < a[pos-1], swap and pos
> 1, decrement pos:
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[3, 2, 5, 4]
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a[pos] < a[pos-1], swap and pos
<= 1, increment pos:
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[2, 3, 5, 4]
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a[pos] >= a[pos-1], increment pos:
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[2, 3, 5, 4]
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a[pos] < a[pos-1], swap and pos
> 1, decrement pos:
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[2, 3, 4, 5]
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a[pos] >= a[pos-1], increment pos:
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[2, 3, 4, 5]
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a[pos] >= a[pos-1], increment pos:
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[2, 3, 4, 5]
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pos == length(a), finished.
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Algorithm
procedure
optimizedGnomeSort(a[])
pos := 1
last := 0
while pos < length(a)
if (a[pos] >= a[pos-1])
if (last != 0)
pos := last
last := 0
end if
pos := pos + 1
else
swap a[pos] and a[pos-1]
if (pos > 1)
if (last == 0)
last := pos
end if
pos := pos - 1
else
pos := pos + 1
end if
end if
end while
end
procedure
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