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

Given a string, return the first recurring letter that appears. If there are no recurring letters, return None.

Example:

Input: qwertty
Output: t

Input: qwerty
Output: None

Here’s some starter code:

def first_recurring_char(s):
  # Fill this in.
  
print(first_recurring_char('qwertty'))
# t

print(first_recurring_char('qwerty'))
# None