Problem 795. Joining Ranges

You are given a n-by-2 matrix. Each row represents a numeric range, e.g.

x = [0 5; 10 3; 20 15; 16 19; 25 25]

contains ranges [0 5], [10 3], [20 15], [16 19], and [25 25]. Note that the first column does not always contain the smaller number. Join all overlapping ranges and return the sorted (both columns and all rows must be sorted) matrix of joined ranges

y = [0 10; 15 20; 25 25]

i.e. ranges [0 5] and [10 3] are combined to [0 10], range [16 19] is completely overlapped by [15 20] and [25 25] is kept because it is a separate range.