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

.

class Solution {
public:
int lengthOfLastWord(const char *s) {
int pre = 0, cur = 0;
while(*s != NULL)
{
if(*s == ' ')
{
pre = cur == 0 ? pre : cur;
cur = 0;
}
else
{
cur++;
}
s++;
}
pre = cur == 0 ? pre : cur;
return pre;
}
};

Round 2:

class Solution {
public:
int lengthOfLastWord(const char *s) {
int r = strlen(s)-1;
int count = 0;
while(r >= 0)
{
if(s[r] != ' ')
{
count++;
}
else if(s[r] == ' ' && count > 0)
break;
r--;
}
return count;
}
};

Round 3:

class Solution {
public:
int lengthOfLastWord(string s) {
int count = 0;
bool flag = false;
for(int i = s.size()-1; i >= 0; i--)
{
if(' ' == s[i])
{
if(false == flag)
{
continue;
}
else if(true == flag)
{
return count;
}
}
else
{
flag = true;
count++;
}
}
return count;
}
};