Clinic #24: Word Search II

Pattern: Trie + backtracking · LC 212

Among its panels is a search drawn as a branching tree, with most of the branches crossed out before anyone walks them. This clinic is that crossing-out, done by a word list that knows when to give up.

Before you start. You need the tree of letters from Trees (BST, balancing, heaps, tries): every word is one path down from the top, one letter per step, and words that start the same way share their first steps; Clinic #23: Implement Trie builds one in code. You also need the move from Algorithm Design Patterns‘s chess queens: make a choice, go deeper, and undo the choice the moment it cannot work.