input: Write a function to find all permutations of a given string.
  assert find_permutations("abc") == ['abc', 'acb', 'bac', 'bca', 'cab', 'cba']
  assert find_permutations("a") == ['a']
  assert find_permutations("ab") == ['ab', 'ba']
output: def find_permutations(s):
      if len(s) == 1:
          return [s]
      
      permutations = []
      for i in range(len(s)):
          for p in find_permutations(s[:i] + s[i+1:]):
              permutations.append(s[i] + p)
      
      return permutations