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

You are given a string of parenthesis. Return the minimum number of parenthesis that would need to be removed in order to make the string valid. "Valid" means that each open parenthesis has a matching closed parenthesis.

Example:

"()())()"

The following input should return 1.

")("

Here's a start:

<pre lang=py>
def count_invalid_parenthesis(string):
  # Fill this in.

print count_invalid_parenthesis("()())()")
# 1
</pre>