Step 4, copy each act of nodes edge list to this array.
So vertex 1 copies its 3 element neighbor list into the output array, starting at offset 0,
and vertex 3 copies its only neighbor to offset 3.
So the potential new frontier here are nodes 0, 2, 4, and 4.
第四步,把节点边界列表的每个行为复制到这个数组。
所以顶点1把它的3个元素邻居列表复制到输出数组,以偏移0作为开始;
顶点3把它唯一的邻居复制到偏移3。
所以这里可能的新边界是节点0、2、4和4