Stooge sort

Class Visualization of Stooge sort (only shows swaps). Sorting algorithm Array O(nlog 3/log 1.5) O(n)

Stooge sort is a recursive sorting algorithm. It is notable for its exceptional bad time complexity of O(nlog 3 / log 1.5 ) = O(n2.7095...). The running time of the algorithm is thus slower compared to reasonable sorting algorithms, and is slower than Bubble sort, a canonical example of a fairly inefficient sort. It is however more efficient than Slowsort. The name comes from The Three Stooges.

The algorithm is defined as follows:

• If the value at the start is larger than the value at the end, swap them.
• If there are 3 or more elements in the list, then:
• Stooge sort the initial 2/3 of the list
• Stooge sort the final 2/3 of the list
• Stooge sort the initial 2/3 of the list again

It is important to get the integer sort size used in the recursive calls by rounding the 2/3 upwards, e.g. rounding 2/3 of 5 should give 4 rather than 3, as otherwise the sort can fail on certain data. However, if the code is written to end on a base case of size 1, rather than terminating on either size 1 or size 2, rounding the 2/3 of 2 upwards gives an infinite number of calls.

Implementation

function stoogesort(array L, i = 0, j = length(L)-1){
if L[i] > L[j] then
L[i]  L[j]
if (j - i + 1) > 2 then
t = (j - i + 1) / 3
stoogesort(L, i  , j-t)
stoogesort(L, i+t, j  )
stoogesort(L, i  , j-t)
return L
}