[Leetcode] 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.
For example,
Given s = "Hello World",
return 5.

    public int lengthOfLastWord(String s) {
        int n = s.length();
        int p1 = n - 1, p2 = n - 1;
        while(p2 >= 0 && s.charAt(p2) == ' ')
            p2--;
        p1 = p2;
        while(p2 >= 0 && s.charAt(p2) != ' ')
            p2--;
        return p1 - p2;
    }