Connecting flights

Problem

Noah booked a trip around South America with several stopovers, and his ticket lists each leg as the code of the city it leaves from and the code of the city it lands in. Before printing it, the travel agent checks that no leg departs from a city he is not in.

Write a function that takes the list of legs, in order, and returns true if every leg leaves from the city where the previous one landed, and false if any does not. Each leg is a string shaped like "MEX-BOG": three capital letters for departure, a hyphen and three letters for arrival, with no spaces.

["MEX-BOG", "BOG-LIM", "LIM-SCL"] is connected: true. In ["MEX-BOG", "LIM-SCL"] he lands in BOG and leaves from LIM: false. Going back to a city he already visited is fine. An empty list, or one with a single leg, is connected.

Examples

• The example

  ["MEX-BOG", "BOG-LIM", "LIM-SCL"] → true

• Both land in the same city

  ["MEX-BOG", "LIM-BOG"] → false

• A single leg

  ["GDL-CUN"] → true

• There and back

  ["MEX-BOG", "BOG-MEX"] → true

Besides these, the challenge has hidden tests that are revealed when you submit your solution.

You start with this

def is_connected(legs):
    pass

function isConnected(legs) {
}