Write a program that, given a set of numbers, returns the gaps between them. A gap should be represented as first missing number and the last one separated by a dash.

Example: "2-3"

The user should be able to add and remove numbers and recalculate the gaps accordingly.

That means you have to implement two methods:

• insert(number)
• remove(number)

For example, after inserting numbers 2, 5, 7 the system should return [ "1-1" , "3-4" , "6-6" ] Then, after removing number 5 the system should return [ "1-1" , "3-6" ]

Both methods accept one number and return an array of 'gaps' represented as strings, as shown above.

Take one step at a time!

1. Insert number 1. Verify that there's no gaps
2. Insert number 2. Verify that there's one gap 1-1
3. Insert number 1 then 2. Verify that there's no gaps
4. Insert numbers 4 then 1. Verify that there's one gap: 2-3
5. Insert numbers 1, 4 then 2. Verify that there's one gap: 3-3
6. Insert numbers 1, 4 then 3. Verify that there's one gap: 2-2
7. Insert numbers 1, 7 then 4. Verify that there's two gaps: 2-3 and 5-6
8. Insert numbers 1, 3 then 2. Verify that there's no gaps

1. Insert number 1, remove number 1. Verify that there's no gaps
2. Insert number 5, remove number 5. Verify that there's no gaps
3. Insert numbers 5, 6, 7, remove number 6. Verify that there's two gaps: 1-4 and 6-6
4. Insert numbers 5, 6, 7, remove number 5. Verify that there's one gap: 1-5
5. Insert numbers 1, 2, 5, remove number 2. Verify that there's one gap: 2-4
6. Insert numbers 1, 3, 5, remove number 3. Verify that there's one gap: 2-4
7. Insert numbers 1, 5, remove number 5. Verify that there's no gaps

1. Output the one-sized gaps as one single number, so 1-1 becomes 1