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

.

这个简单的题目花了不少时间，各种出错。后来发现“a ”通过不了，最后在for循环之前加了一个while先去掉最后的空格 通过。

class Solution {
public:
int lengthOfLastWord(string s) {
int num=0;
if (s.length()) {
int r = s.length()-1;
while (s[r]==' ') {
r--;
}
for ( ; r>=0; r--) {
if(s[r]==' '){
break;
}
num++;
}
}
return num;

}
};