 class="comment">// // Group the nodes in the same connected component together.</span></div>
<div class="line"><a name="l00058"></a><span class="lineno">   58</span>&#160;<span class="comment">// // group[class_number][i] contains the i-th node in group class_number.</span></div>
<div class="line"><a name="l00059"></a><span class="lineno">   59</span>&#160;<span class="comment">// hash_map&lt;int, vector&lt;int&gt; &gt; group(num_connected_components);</span></div>
<div class="line"><a name="l00060"></a><s