58. 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.
Given s = "Hello World",
Preprocess the input string first, remove the spaces at the beginning and the end, and then use a counter to accumulate the length of the non-space string, and clear the counter when it encounters a space.