TopCoder problem "SwimmersDelight" used in SRM 266 (Division II Level One)

Problem Statement

    You want to cross a river 10 feet wide and there are 2 stones in the water you can jump on. A few jumps are needed, but your only concern is the longest one. This is obviously the most problematic, so you wish to choose a path that makes this jump as small as possible.

The length of a jump between two stones of coordinates (x1,y1) and (x2,y2) is defined as the Euclidian distance:

  sqrt((x1 - x2) * (x1 - x2)  +  (y1 - y2) * (y1 - y2))

You will be given a int[] x and a int[] y with exactly 2 elements each, representing the coordinates of the stones: (x[i],y[i]) is the location of the i-th stone. The edge of the shore on which you initially stand has an x-value of 0 and could take any y-value. Thus, the minimal distance between the shore and the first stone you jump on is the x-value in the location of that stone. The edge of the other shore has an x-value of 10 and could take any y-value as well.

Return the distance of the longest jump you need to make, rounded to the nearest integer.


Parameters:int[], int[]
Method signature:int longestJump(int[] x, int[] y)
(be sure your method is public)


-You may jump on the 2 stones in any order, or just on one stone.


-x and y will each contain 2 elements.
-All values in x are between 1 and 9, inclusive.
-All values in y are between 0 and 10, inclusive.
-The two stones are not in the same location.
-No actual distance will be more than 1e-4 close to some integer + 0.5.


Returns: 4
The three stones are arranged in a line, so the strategy is quite simple here: you first jump on the stone at (3,5), then on the stone at (7,5) and you finally reach the other shore at (10,5). The longest jump has a length of 4 feet: from (3,5) to (7,5).

If you like to play around, you can follow the path (0,5) - (7,5) - (3,5) - (10,5), but this is not optimal since you have to make a jump of 7 feet!

Thus, the correct answer is 4.
Returns: 4
The path you should take is (0,5) - (3,5) - (6,2) - (10,2). Between (3,5) and (6,2) there is a distance of sqrt(3*3 + 3*3) = 4.2426. There are no jumps longer than this and because the answer is rounded to the nearest integer, you should return 4.
Returns: 9
If you can jump 9 feet at once, chances are you are also a good swimmer ...
Returns: 7
Only the stone at (3,0) is used in this case. The stone at (8,10) is more than 7 feet away from both the shore and the stone at (3,0).
Returns: 6
The river can be a good initiation in the triple-jump technique. But you can also skip the stone at (2,5), as you need to take a 6 feet jump anyway.

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PabloGilberto , brett1479 , Olexiy

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