This question is similar to the question where arrival and departure time of trains are given and we have to calculate minimum no of platforms required. The logic is whenever job start/train comes cont++ when depart/end counnt-- then the maxm value of count in bw will be the ans.Note at the end count=0
eg . as, bs be,cs,ce,ae
count: 1. 2 . 1 . 2. 1 .0
maxm value of count is 2 so two platforms/room req.