Given an array intervals where intervals[i] = [l _i , r _i ] represent the interval [l _i , r _i ) , remove all intervals that are covered by another interval in the list.
The interval [a, b) is covered by the interval [c, d) if and only if c <= a and b <= d .
Return the number of remaining intervals .
1 <= intervals.length <= 1000intervals[i].length == 20 <= l _i < r _i <= 10 ^5All the given intervals are unique .