Are they consecutive?

Problem

Tickets 14, 12, 15 and 13 are consecutive: line them up and they come one after another with no gaps.

Write a function that takes a list of whole numbers and returns true if they are consecutive and false if they are not.

The rules: the order they come in does not matter. None of the numbers along the way can be missing, so 1, 2, 3, 5 and 6 are not consecutive. No number can repeat either: 1, 2 and 1 are not consecutive, because the 1 shows up twice. Negatives count too. A single number is consecutive, and with an empty list you return false.

Examples

• One after another

  [1, 2, 3, 4, 5] → true

• The 4 is missing

  [1, 2, 3, 5, 6] → false

• A repeat

  [1, 2, 1] → false

• Out of order

  [14, 12, 15, 13] → true

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

You start with this

def are_consecutive(numbers):
    pass

function areConsecutive(numbers) {
}