2884	 Permutation Enumeration Four New Permutation Algorithms	 Classical permutation enumeration algorithms encounter special cases requiring additional computation every nth permutation when generating the n permutations on n marks. Four new algorithms have the attribute that special cases occur every n n- permutations. Two of the algorithms produce the next permutation with a single exchange of two marks. The other two algorithms infrequently exchange more than two marks but the rules for generating the next permutation are very simple. Performance tests which have counted execution of assignment statements comparisons arithmetic operations and subscripted array references have shown superiority of the new algorithms compared to Boothroyd s implementation of M. B. Well s algorithm and Ehrlich s implementation of the Johnson-Trotter algorithm. permutations loop-free algorithms
