Hi, here's your problem today. This problem was recently asked by Amazon:

You are given a 2D array of characters, and a target string. Return whether or not the word target word exists in the matrix. Unlike a standard word search, the word must be either going left-to-right, or top-to-bottom in the matrix.

Example:

<pre lang=py>
[['F', 'A', 'C', 'I'],
 ['O', 'B', 'Q', 'P'],
 ['A', 'N', 'O', 'B'],
 ['M', 'A', 'S', 'S']]
</pre>

Given this matrix, and the target word FOAM, you should return true, as it can be found going up-to-down in the first column.

Here's the function signature:

<pre lang=py>
def word_search(matrix, word):
  # Fill this in.
  
matrix = [
  ['F', 'A', 'C', 'I'],
  ['O', 'B', 'Q', 'P'],
  ['A', 'N', 'O', 'B'],
  ['M', 'A', 'S', 'S']]
print word_search(matrix, 'FOAM')
# True
</pre>