Minimum Spanning Trees

There are n cities labeled 1..n. You are given connections, where connections[i] = [a, b, cost] is the cost to build a bidirectional link between city a and city b. Return the minimum total cost to connect all n cities so that every city is reachable from every other. If it is impossible to connect them all, return -1.

There are n houses labeled 1..n. You can supply water to a house either by building a well on it — wells[i - 1] is the cost of a well at house i — or by laying a pipe from another supplied house, where pipes[j] = [house1, house2, cost] is the cost of a bidirectional pipe (multiple pipes may connect the same pair). Return the minimum total cost to supply water to every house.