leetcode_length of last word_easy

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.

简单从尾部找下即可，注意边界。

class Solution {public:    int lengthOfLastWord(const char *s) {        int slen=strlen(s),len=0;        if(slen<=0)            return 0;        int i=slen-1;        while(s[i]==' '&&i>0)            i--;        for(; i>=0; i--)        {            if(isalpha(s[i]))                len++;            else if(s[i]==' ')                break;        }            return len;    }};