<p>You are given a string <code>s</code>. Reorder the string using the following algorithm:</p>

<ol>
	<li>Remove the <strong>smallest</strong> character from <code>s</code> and <strong>append</strong> it to the result.</li>
	<li>Remove the <strong>smallest</strong> character from <code>s</code> that is greater than the last appended character, and <strong>append</strong> it to the result.</li>
	<li>Repeat step 2 until no more characters can be removed.</li>
	<li>Remove the <strong>largest</strong> character from <code>s</code> and <strong>append</strong> it to the result.</li>
	<li>Remove the <strong>largest</strong> character from <code>s</code> that is smaller than the last appended character, and <strong>append</strong> it to the result.</li>
	<li>Repeat step 5 until no more characters can be removed.</li>
	<li>Repeat steps 1 through 6 until all characters from <code>s</code> have been removed.</li>
</ol>

<p>If the smallest or largest character appears more than once, you may choose any occurrence to append to the result.</p>

<p>Return the resulting string after reordering <code>s</code> using this algorithm.</p>

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

<pre>
<strong>Input:</strong> s = &quot;aaaabbbbcccc&quot;
<strong>Output:</strong> &quot;abccbaabccba&quot;
<strong>Explanation:</strong> After steps 1, 2 and 3 of the first iteration, result = &quot;abc&quot;
After steps 4, 5 and 6 of the first iteration, result = &quot;abccba&quot;
First iteration is done. Now s = &quot;aabbcc&quot; and we go back to step 1
After steps 1, 2 and 3 of the second iteration, result = &quot;abccbaabc&quot;
After steps 4, 5 and 6 of the second iteration, result = &quot;abccbaabccba&quot;
</pre>

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

<pre>
<strong>Input:</strong> s = &quot;rat&quot;
<strong>Output:</strong> &quot;art&quot;
<strong>Explanation:</strong> The word &quot;rat&quot; becomes &quot;art&quot; after re-ordering it with the mentioned algorithm.
</pre>

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

<ul>
	<li><code>1 &lt;= s.length &lt;= 500</code></li>
	<li><code>s</code> consists of only lowercase English letters.</li>
</ul>

class Solution {
public:
    string sortString(string s) {
        // sort(s.begin(), s.end());
        string str = "";
        unordered_map<char, int> mp;
        for(auto it:s){
            mp[it]++;
        }
        vector<pair<char, int>> v;
        for(auto it:mp){
            v.push_back({it.first, it.second});
        }
        sort(v.begin(), v.end());
        // string str="";
        int n=s.length();
        while(1){
            if(n==0){
                break;
            }
            for(int i=0;i<v.size();i++){
                if(n==0){
                    break;
                }
                if(v[i].second > 0){
                    str += v[i].first;
                    v[i].second--; n--;
                }
    
            }
            if(n==0){
                break;
            }
            for(int i=v.size()-1;i>=0;i--){
                if(n==0){
                    break;
                }
                if(v[i].second > 0){
                    str += v[i].first;
                    v[i].second--;n--;
                }
            }
            if(n==0){
                break;
            }
        }
        return str;
    }
};
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