Given a string
s consists of upper/lower-case alphabets and empty space characters
' ', return the length of last word in the string.
If the last word does not exist, return
Note: A word is defined as a character sequence consists of non-space characters only.
s = "Hello World",
length("World") = 5.
Please make sure you try to solve this problem without using library functions. Make sure you only traverse the string once.