Cities and Roads

I will give you the Cities and Roads task. You get $N$ cities and some roads, and you must add the fewest roads to make the graph connected. If the graph has $K$ connected components, you need $K-1$ roads to join them into one piece.

You can solve it by running a traversal from each unvisited node, counting components, and outputting the count minus one. You will use the same traversal idea in the next sections, so this problem sets your target.