Radix Sorting with No Extra Space

It is well known that n integers in the range [1, nc ] can be sorted in O(n) time in the RAM model using radix sorting. More generally, integers in any range [1, U] can be sorted in O(n √ log log n) time [5]. However, these algorithms use O(n) words of extra memory. Is this necessary? We present a simple, stable, integer sorting algorithm for words of size O(log n), which works in O(n) time and uses only O(1) words of extra memory on a RAM model. This is the integer sorting case most useful in practice. We extend this result with same bounds to the case when the keys are read-only, which is of theoretical interest. Another interesting question is the case of arbitrary c. Here we present a black-box transformation from any RAM sorting algorithm to a sorting algorithm which uses only O(1) extra space and has the same running time. This settles the complexity of in-place sorting in terms of the complexity of sorting.

• Type: Conference
• Year: 2007
• Where: ESA
• Authors: Gianni Franceschini, S. Muthukrishnan, Mihai Patrascu
• Keywords: Algorithm, ESA 2007, RAM Model, Sorting Algorithm