input: Write a python function to find the longest common prefix among a list of strings.
  assert longestCommonPrefix(['car', 'cat', 'cow']) == 'c'
  assert longestCommonPrefix(['flower', 'flow', 'flight']) == 'fl'
  assert longestCommonPrefix(['dog', 'racecar', 'car']) == ''
  assert longestCommonPrefix(['apple', 'ape', 'april']) == 'ap'
output: def longestCommonPrefix(strs):
      if not strs:
          return ""
      
      prefix = strs[0]
      
      for string in strs[1:]:
          while string[:len(prefix)] != prefix and prefix:
              prefix = prefix[:-1]
      
      return prefix