Design a Python algorithm to parse a list of strings and prints the longest string's length.
listOfString= ["I", "am", "so", "happy"]
listStrings= ["I", "am", "so", "happy"]
longestStringLen = 0
for string in listStrings:
    if (len(string) > longestStringLen):
        longestStringLen = len(string)

print(longestStringLen)