[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.

指针相减

class Solution {
public:
    int lengthOfLastWord(const char *s) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if (s == NULL)
            return 0;
            
        const char *start = s;
        int len = 0;
        while(*s != '\0')
        {
            if (*s == ' ')
            {
                int l = s - start;                
                if (l != 0)
                    len = l;
                start = s + 1;
                s++;
            }
            else
                s++;
        }
        
        int l = s - start;
        if (l != 0)
            len = l;
            
        return len;
    }
};

模拟题，每次要记录的是空格前的字符开始索引，然后遇到空格得出单词长度。最后要注意的是，可能整个字符没有空格，或者最后一个不是空格，退出循环时要检测一下。

class Solution {
public:
    int lengthOfLastWord(const char *s) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if (s == NULL)
            return 0;
            
        int start = -1;
        int index = 0;
        int len = 0;
        while(*s != '\0')
        {
           if (isalpha(*s) && start == -1)
               start = index;
               
           if (isspace(*s) && start != -1)
           {
               len = index - start;
               start = -1;
           }
           
           s++;
           index++;
        }
        
        if (start != -1)
            len = index - start;
        
        return len;
    }
};