Write a function called sumIntervals that accepts an array of intervals, and returns the sum of all the interval lengths.
Overlapping intervals should only be counted once.
Intervals are represented by a pair of integers in the form of an array. The first value of the interval will always be less than the second value. Interval example: [1, 5] is an interval from 1 to 5. The length of this interval is 4.
List containing overlapping intervals:
[
[1,4],
[7, 10],
[3, 5]
]
The sum of the lengths of these intervals is 7. Since [1, 4] and [3, 5] overlap, we can treat the interval as [1, 5], which has a length of 4.
sumIntervals( [
[1,2],
[6, 10],
[11, 15]
] ); //=> returns 9
sumIntervals( [
[1,4],
[7, 10],
[3, 5]
] ); //=> returns 7
sumIntervals( [
[1,5],
[10, 20],
[1, 6],
[16, 19],
[5, 11]
] ); //=> returns 19