<p>Two strings, <code>X</code> and <code>Y</code>, are considered similar if either they are identical or we can make them equivalent by swapping at most two letters (in distinct positions) within the string <code>X</code>.</p>
<p>For example, <code>"tars"</code> and <code>"rats"</code> are similar (swapping at positions <code>0</code> and <code>2</code>), and <code>"rats"</code> and <code>"arts"</code> are similar, but <code>"star"</code> is not similar to <code>"tars"</code>, <code>"rats"</code>, or <code>"arts"</code>.</p>
<p>Together, these form two connected groups by similarity: <code>{"tars", "rats", "arts"}</code> and <code>{"star"}</code>. Notice that <code>"tars"</code> and <code>"arts"</code> are in the same group even though they are not similar. Formally, each group is such that a word is in the group if and only if it is similar to at least one other word in the group.</p>
<p>We are given a list <code>strs</code> of strings where every string in <code>strs</code> is an anagram of every other string in <code>strs</code>. How many groups are there?</p>
