The adaptive sorting problem is defined as any sorting algorithm with its run time proportional to the disorder of the input sequence X. Estivill-Castro et al (Estivill-Castro & Wood 1992) define an operation inv(X) to measure the disorder of X, where inv(X) denotes the exact number of inversions in X. (i,j) is an inversion if i < j and xi > xj. The number of inversions is at most (n 2) for any sequence, therefore any exchange sorting algorithm must terminate after O(n2) element swaps. Clearly INSERTION SORT belongs to the adaptive sorting family as it performs exactly inv(X)+n−1 comparisons and inv(X)+2n−1 data moves.