Length of Last Word

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 0.

Note: A word is defined as a character sequence consists of non-space characters only.

Example:

Given s = "Hello World",

return 5 as length("World") = 5.

Please make sure you try to solve this problem without using library functions. Make sure you only traverse the string once.