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.

//采用双指针的思想，两个指针的间隔距离就是last word的长度
public class Solution {
    public int lengthOfLastWord(String s) {
        
        if(s==null || s.length()==0){        //不存在last word
            return 0;
        }
        
        int tailPointer = s.length()-1;      //尾指针
        while(tailPointer>=0 && s.charAt(tailPointer)==' '){   //从后向前过滤掉所有空格
            tailPointer--;
        }
        
        //注意，此处是可能为-1的，但是Java采用不完全计算来求bool值的，因而下面的while中
        //s.charAt(headPointer)不会出现index溢出的情况，且return (-1)-(-1)=0
        
        int headPointer = tailPointer;
        while(headPointer>=0 && s.charAt(headPointer)!=' '){   //从后向前找到第一个空格
            headPointer--;
        }
        
        return (tailPointer - headPointer);
    }
}