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Ivan Li.  #Max = 9  Mean (attempted) = 39.4 42.

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Presentation on theme: "Ivan Li.  #Max = 9  Mean (attempted) = 39.4 42."— Presentation transcript:

1 Ivan Li

2  #Max = 9  Mean (attempted) = 39.4 42

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

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

5  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

6  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 )

7  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!

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


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