<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 {
 private:
  vector<int> parent;
  vector<int> rank;

 public:
  int find(int x) {
    if (parent[x] == x) return x;
    return parent[x] = find(parent[x]);
  }
  void join(int x, int y) {
    int p1 = find(x);
    int p2 = find(y);
    if (p1 != p2) {
      if (rank[p1] > rank[p2]) {
        parent[p2] = p1;
      } else if (rank[p1] < rank[p2]) {
        parent[p1] = p2;
      } else {
        parent[p2] = p1;
        rank[p2]++;
      }
    }
  }
  string smallestStringWithSwaps(string s, vector<vector<int>> &pairs) {
    int n = s.length();
    parent.resize(n);
    rank.resize(n);
    for (int i = 0; i < n; ++i) {
      parent[i] = i;
      rank[i] = 1;
    }

    for (auto pair : pairs) {
      int a = pair[0];
      int b = pair[1];
      join(a, b);
    }

    unordered_map<int, vector<int>> group_index;
    for (int i = 0; i < n; ++i) {
      group_index[find(i)].push_back(i);
    }

    for (const auto &[key, indices] : group_index) {
      string sub_string;
      for (auto index : indices) {
        sub_string.push_back(s[index]);
      }
      sort(sub_string.begin(), sub_string.end());
      for (int i = 0; i < indices.size(); ++i) {
        s[indices[i]] = sub_string[i];
      }
    }

    return s;
  }
};
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