Find All Words on a Board

Given a 2D board of characters and an array of words, find all the words in the array that can be formed by tracing a path through adjacent cells in the board. Adjacent cells are those which horizontally or vertically neighbor each other. We can't use the same cell more than once for a single word.

Example:

Input: board = [['b', 'y', 's'], ['r', 't', 'e'], ['a', 'i', 'n']],
       words = ['byte', 'bytes', 'rat', 'rain', 'trait', 'train']
Output: ['byte', 'bytes', 'rain', 'train']