Stooge sort

Stooge sort is a recursive sorting algorithm with a time complexity of O(n^{log 3 / log 1.5} ) = O(n^2.7095...). The running time of the algorithm is thus slower compared to efficient sorting algorithms, such as Merge sort, and is even slower than Bubble sort, a canonical example of a fairly inefficient and simple sort.

The algorithm is defined as follows:

• If the value at the end is smaller than the value at the start, 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[j] < L[i] 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

References

• Black, Paul E. "stooge sort". Dictionary of Algorithms and Data Structures. National Institute of Standards and Technology. Retrieved 2011-06-18. 
• Cormen, Thomas H.; Leiserson, Charles E.; Rivest, Ronald L.; Stein, Clifford (2001) [1990]. "Problem 7-3". Introduction to Algorithms (2nd ed.). MIT Press and McGraw-Hill. pp. 161–162. ISBN 0-262-03293-7. 

External links

• Everything2.com – Stooge sort
• Sorting Algorithms (including Stooge sort)
• Stooge sort – implementation and comparison