Ivan Li

 #Max = 9  Mean (attempted) =

 A car travels to the South  If it reaches a road, follow its direction  Find the number of roads visited

 The travel direction is S, E or W ◦ Cannot go North!  There are polar bears in the South ◦ In zoos =]

 Whether a car will reach a road on the south depends on the x coordinates of the car and the start and end points of the road ◦ (x1 ≤ x and x ≤ x2) or (x2 ≤ x and x ≤ x1) ◦ (x1-x)*(x2-x) ≤ 0  Cool but risky =]  After the car finishes travelling on a road, its position is in the end point

 For each road, check if the car will hit it if the car go straight ◦ Road on the south of the car? ◦ Check x coordinates?  If it will, calculate the time (difference in y coordinates) the car will hit the road  Then go hit the road with min time!  Repeat the process until the car hit no roads  O(n 2 )

 After the car has passed a road ◦ i.e. y coordinates of car smaller than road ◦ Then we can ignore the road sayonara!!!  When the car has y coordinate equals that of a road ◦ Hit or miss ◦ Hit: change the position of the car, bye to the road ◦ Miss: Just bye to the road  The y coordinates of the car won’t increase ◦ The car must visit the roads in y order ◦ The input is sorted!

 Keep the index of the last road not passed  Hit or Miss?  Increment the index  Complexity O(n)