<p>Given an input string <code>s</code>, reverse the order of the <strong>words</strong>.</p>

<p>A <strong>word</strong> is defined as a sequence of non-space characters. The <strong>words</strong> in <code>s</code> will be separated by at least one space.</p>

<p>Return <em>a string of the words in reverse order concatenated by a single space.</em></p>

<p><b>Note</b> that <code>s</code> may contain leading or trailing spaces or multiple spaces between two words. The returned string should only have a single space separating the words. Do not include any extra spaces.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;the sky is blue&quot;
<strong>Output:</strong> &quot;blue is sky the&quot;
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;  hello world  &quot;
<strong>Output:</strong> &quot;world hello&quot;
<strong>Explanation:</strong> Your reversed string should not contain leading or trailing spaces.
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;a good   example&quot;
<strong>Output:</strong> &quot;example good a&quot;
<strong>Explanation:</strong> You need to reduce multiple spaces between two words to a single space in the reversed string.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= s.length &lt;= 10<sup>4</sup></code></li>
	<li><code>s</code> contains English letters (upper-case and lower-case), digits, and spaces <code>&#39; &#39;</code>.</li>
	<li>There is <strong>at least one</strong> word in <code>s</code>.</li>
</ul>

<p>&nbsp;</p>
<p><b data-stringify-type="bold">Follow-up:&nbsp;</b>If the string data type is mutable in your language, can&nbsp;you solve it&nbsp;<b data-stringify-type="bold">in-place</b>&nbsp;with&nbsp;<code data-stringify-type="code">O(1)</code>&nbsp;extra space?</p>

class Solution {
public:
    string revs(string s, int x, int y){
        string res = s.substr(x, y-x);
        reverse(res.begin(), res.end());
        return res;
    }
    string removespace(string s){
        int slow = 0;
        bool flag = false;
        string res;
        for(int fast = 0; fast < s.size(); fast++){
            if(flag == true && s[fast] ==' '){
                flag = false;
                res += ' ';
            }
            else if(s[fast] != ' '){
                flag = true;
                res += s[fast];
            }
        }
        if(s[s.size() - 1]==' '){int size = res.size() - 1;
        res.resize(size);}
        return res;
    }
    string reverseWords(string s) {
        string res;
        s = removespace(s);
        reverse(s.begin(), s.end());
        int i = 0;
        while(i < s.size()){
            int left = i;
            while(i < s.size() && s[i] != ' '){
                i++;
            }
            int right = i;
            string tmp = revs(s, left, right);
            res += tmp;
            res += ' ';
            i++;
        }
        int size = res.size() - 1;
        res.resize(size);
        return res;

    }
};
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