sumIntervals( [
[1,2],
[6, 10],
[11, 15]
] ) => 9
sumIntervals( [
[1,4],
[7, 10],
[3, 5]
] ) => 7
sumIntervals( [
[1,5],
[10, 20],
[1, 6],
[16, 19],
[5, 11]
] ) => 19
sumIntervals( [
[0, 20],
[-100000000, 10],
[30, 40]
] ) => 100000030
👉 @seniorFront