In the interval covering problem, we are given n
intervals
[s1,t1), [s2,t2), ···, [sn,tn)
such that
S i∈[n][si,ti) = [0,T).
The goal of the problem is to return a smallest-size set
S ⊆ [n]
such that
S i∈S[si,ti) = [0,T).
Design a greedy algorithm for this problem.