Problem

Given a list of non-overlapping intervals intervals sorted by their starting values, insert a new interval and merge any overlapping intervals.

The result should be a list of non-overlapping intervals sorted by starting values.

Examples

addInterval([[1,4],[7,8]], [2,6])
// [[1,6],[7,8]]

addInterval([[1,2],[3,4],[5,6],[7,8]], [5,8])
// [[1,2],[3,4],[5,8]]