Find the Words in the Grid

A word puzzle shows a grid of letters, given as a list of equal-length strings. A word can be traced in the grid if you can start on a square holding its first letter and reach each next letter on a square directly above, below, left or right of the previous one, never using the same square twice within the word.

Write find_words(grid, words) that returns the alphabetically sorted list of the words in words that can be traced. Each word appears once in the result, even if words lists it twice.

Examples

grid = [
    'snow',
    'tale',
    'ripe',
]
find_words(grid, ['snow', 'stair', 'plan', 'peel', 'tail', 'wee', 'owl', 'pale'])
# returns ['peel', 'plan', 'snow', 'stair', 'wee']

find_words(['ab', 'ba'], ['ababa', 'abab', 'bab'])
# returns ['abab', 'bab']

In the first grid, "stair" goes down from s to t, right to a, down to i and left to r. "tail" cannot be traced because the only i is not next to the only l. In the second grid "ababa" would need a fifth square, and squares cannot be used twice.

Constraints

• The grid has 1 to 12 rows and 1 to 12 columns of lowercase letters.
• words has 0 to 5,000 words, each with 1 to 10 lowercase letters.