Word Search II Solution

Implement the complete solution with trie-guided backtracking. Implementation steps:

$1.$ Build trie from word list

$2.$ For each cell, start DFS with trie root

$3.$ Track visited cells (modify board or use set)

$4.$ When reaching a word-end node, add to results

$5.$ Backtrack by restoring cell state Common bugs:

• Forgetting to unmark visited cells when backtracking
• Finding the same word multiple times (from different starting positions)
• Not handling the case where one word is a prefix of another

Time: $O(M \cdot N \cdot 4^L)$ where $M \times N$ is board size and $L$ is max word length. Trie pruning makes this much faster in practice.