[LintCode] Reverse Words in a String 翻转字符串中的单词

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

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

Have you met this question in a real interview? 

Yes

Clarification

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

LeetCode上的原题，请参见我之前的博客Reverse Words in a String。

解法一：

class Solution {
public:
    /**
     * @param s : A string
     * @return : A string
     */
    string reverseWords(string s) {
        int storeIndex = 0, n = s.size();
        reverse(s.begin(), s.end());
        for (int i = 0; i < n; ++i) {
            if (s[i] != ' ') {
                if (storeIndex != 0) s[storeIndex++] = ' ';
                int j = i;
                while (j < n && s[j] != ' ') s[storeIndex++] = s[j++];
                reverse(s.begin() + storeIndex - (j - i), s.begin() + storeIndex);
                i = j;
            }
        }
        return string(s.begin(), s.begin() + storeIndex);
    }
};

解法二：

class Solution {
public:
    /**
     * @param s : A string
     * @return : A string
     */
    string reverseWords(string s) {
        string res = "", t = "";
        istringstream is(s);
        while (getline(is, t, ' ')) {
            if (t.empty()) continue;
            res = (res.empty() ? t : (t + " " + res));
        }
        return res;
    }
};

解法三：

class Solution {
public:
    /**
     * @param s : A string
     * @return : A string
     */
    string reverseWords(string s) {
        istringstream is(s);
        is >> s;
        string t; 
        while (is >> t) {
            s = t + " " + s;
        }
        return (s[0] == ' ') ? "" : s;
    }
};