Using this arrangement is equivalent to implementing each R-way trie node as a binary search tree that uses as keys the characters corresponding to non-null links. By contrast, ALGORITHM 5.4 uses a key-indexed array. A TST and its corresponding trie are illustrated above. Continuing the correspondence described in CHAPTER 3 between binary search trees and sorting algorithms, we see that TSTs correspond to 3-way string quicksort in the same way that BSTs correspond to quicksort and tries correspond to MSD sorting. The figures on page 714 and 721, which show the recursive call structure for MSD and 3-way string quicksort (respectively), correspond precisely to the trie and TST drawn on page 746 for that set of keys. Space for links in tries corresponds to the space for counters in string sorting; 3-way branching provides an effective solution to both problems