leetcode Online Judge 150题 解答分析之一 Reverse Words in a String

问题

Given an input string, reverse the string word by word.

For example, Given s = "the sky is blue", return "blue is sky the".

面试时我应该至少问的问题

1. What constitutes a word? A sequence of non-space characters constitutes a word.
2. Could the input string contain leading or trailing spaces? Yes. However, your reversed string should not contain leading or trailing spaces.
3. How about multiple spaces between two words? Reduce them to a single space in the reversed string.

 我大概想了下，但是没有问出来，需要改进！

代码分析

class Solution {
public:
    static void reverseWords(string &s) 
    {
        int len = s.length();
        string result;
        for(int i= len - 1; i >= 0; )
        {
            int lastend = 0;
            while(i >= 0 && s[i] == ' ') //需要先判断i >=0，否则s[i]会出错
            {
                i--;
            }
            if(i < 0) //这里需要break，因为可能一连串的空格，没有任何字母，这时就应该及时退出
                break;
            lastend = i;
            while(i >= 0 && s[i] != ' ') //这里也一样，需要先保证i在合法范围，再访问s[i]
            {
                i--;
            }
            
            if(i <= lastend) // i may be -1
            {
                if(!result.empty())
					result.append(" "); // 至少有一个字符串时，需要添加空格
				result.append(s.substr(i+1, lastend - i));
            }
        }
        
		s.assign(result);
    }
};