input: Write a python function to find the longest common prefix from a list of strings.
  assert commonPrefix(["apple", "ape", "app", "application"]) == "ap"
  assert commonPrefix(["flower", "flow", "flight"]) == "fl"
  assert commonPrefix(["dog", "racecar", "car"]) == ""
output: def commonPrefix(strs):
      if not strs:
          return ""
      prefix = strs[0]
      for s in strs[1:]:
          while not s.startswith(prefix):
              prefix = prefix[:-1]
              if not prefix:
                  return ""
      return prefix