input: Write a function to check if two strings are permutations of each other.
  assert is_permutation("abc", "bca") == True
  assert is_permutation("abc", "abcd") == False
  assert is_permutation("listen", "silent") == True
  assert is_permutation("apple", "papel") == True
  assert is_permutation("rat", "car") == False
output: def is_permutation(str1, str2):
      if len(str1) != len(str2):
          return False
      return sorted(str1) == sorted(str2)