<p>You are given a string <code>s</code>, and an array of pairs of indices in the string&nbsp;<code>pairs</code>&nbsp;where&nbsp;<code>pairs[i] =&nbsp;[a, b]</code>&nbsp;indicates 2 indices(0-indexed) of the string.</p>

<p>You can&nbsp;swap the characters at any pair of indices in the given&nbsp;<code>pairs</code>&nbsp;<strong>any number of times</strong>.</p>

<p>Return the&nbsp;lexicographically smallest string that <code>s</code>&nbsp;can be changed to after using the swaps.</p>

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

<pre>
<strong>Input:</strong> s = &quot;dcab&quot;, pairs = [[0,3],[1,2]]
<strong>Output:</strong> &quot;bacd&quot;
<strong>Explaination:</strong> 
Swap s[0] and s[3], s = &quot;bcad&quot;
Swap s[1] and s[2], s = &quot;bacd&quot;
</pre>

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

<pre>
<strong>Input:</strong> s = &quot;dcab&quot;, pairs = [[0,3],[1,2],[0,2]]
<strong>Output:</strong> &quot;abcd&quot;
<strong>Explaination: </strong>
Swap s[0] and s[3], s = &quot;bcad&quot;
Swap s[0] and s[2], s = &quot;acbd&quot;
Swap s[1] and s[2], s = &quot;abcd&quot;</pre>

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

<pre>
<strong>Input:</strong> s = &quot;cba&quot;, pairs = [[0,1],[1,2]]
<strong>Output:</strong> &quot;abc&quot;
<strong>Explaination: </strong>
Swap s[0] and s[1], s = &quot;bca&quot;
Swap s[1] and s[2], s = &quot;bac&quot;
Swap s[0] and s[1], s = &quot;abc&quot;
</pre>

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

<ul>
	<li><code>1 &lt;= s.length &lt;= 10^5</code></li>
	<li><code>0 &lt;= pairs.length &lt;= 10^5</code></li>
	<li><code>0 &lt;= pairs[i][0], pairs[i][1] &lt;&nbsp;s.length</code></li>
	<li><code>s</code>&nbsp;only contains lower case English letters.</li>
</ul>

class Solution {
public:
    string smallestStringWithSwaps(string s, vector<vector<int>>& pairs) {
        UnionSet groups(s.size());
        for (int  i = 0 ; i < pairs.size() ; i++)
        {
            groups.connect(pairs[i][0], pairs[i][1]);
        }
        
        unordered_map<int, vector<int>> classification;
        for (int i = 0; i < s.size(); i++)
        {
            int root = groups.find(i);
            classification[root].push_back(i);
        }
        
        string ret(s.size(), 'a');
        Comparer comparer(s);
        for (int i = 0; i < classification.size(); i++)
        {
            vector<int> indices(classification[i]);
            sort(indices.begin(), indices.end());
            
            sort(classification[i].begin(), classification[i].end(), comparer);
            for (int j = 0; j < classification[i].size(); j++)
            {
                ret[indices[j]] = s[classification[i][j]];
            }
        }
        
        return ret;
    }

private:
    
    class Comparer
    {
        private:
            string_view sv;
        
        public:
            Comparer(const string& s) : sv(s)
            {
                
            }

            bool operator()(const int& i, const int& j)
            {
                return sv[i] < sv[j];
            }
    };

class UnionSet{

    public:
        UnionSet(int size): rank(size,0), root(size,0), count(size)
        {
            for (int  i = 0 ; i < size; i++)
            {
                root[i] = i;
            }
        }
    
        int find(int i)
        {
            if (i == root[i])
                return i;
            
            root[i] = find(root[i]);
            return root[i];
        }
        
        int getCount()
        {
            return count;
        }
        
        bool connect(int i, int j)
        {
            int rootI = find(i);
            int rootJ = find(j);
            if (rootI == rootJ)
                return false;
            
            if (rank[rootI] > rank[rootJ])
                root[rootJ] = rootI;
            else if (rank[rootJ] > rank[rootI])
                root[rootI] = rootJ;
            else
            {
                root[rootI] = rootJ;
                rank[rootI]++;
            }
            
            count--;
            return true;
        }
          
    private:
        vector<int> rank;
        vector<int> root;
        int count;
    };
};
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