There is a museum. We know some information: there were G guards on D days.
We know the guards workdays with the starting and finishing days.

For example
D=6
G=5
1 - 3
6 - 6
1 - 2
2 - 3
3 - 4

Questions (with answering the example):

1. How long was the longest peroid when the guard worked in museum? (Length of the longest period)
answer: 3

2. How many guards were in the museum?
answer: 2 3 3 1 0 1

3. On which day did the most guard work? if there are more just need the first? max pick
answer: 2

4. What is the start day and the end day when less than 2 guards worked in the museum? max pick but need calculate periods again
answer: 4 - 6
//start 4th end 6th but need check every days