st</span><span class="p">(</span><span class="n">graph</span><span class="o">.</span><span class="n">nodes</span><span class="p">())[</span><span class="mi">0</span><span class="p">]</span>
    <span class="n">queue</span> <span class="o">=</span> <span class="p">[(</span><span class="n">start_index</span><span class="p">,</span> <span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">0</span><span class="p">),</span>
     