Leetcode: Length of Last Word in C++

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.

Solution:

public int lengthOfLastWord(String s) {
        int pre = -1;
        int len = s.length();
        if(len==0)
        return 0;
        int p =0;
        int end = len-1;
        while(end>0&&s.charAt(end)==' ')
            end--;
        while(p<=end)
        {
            if(s.charAt(p)==' ')
              pre = p;
            p++;
        }
        return end - pre;
    }