###### 编程介的小学生

2017-11-30 16:10 阅读 832

# The shortest path

Problem Description
There are n points on the plane, Pi(xi, yi)(1 <= i <= n), and xi < xj (i Before you reach the rightmost point Pn, you can only visit the points those have the bigger x-coordinate value. For example, you are at Pi now, then you can only visit Pj(j > i). When you reach Pn, the rule is changed, from now on you can only visit the points those have the smaller x-coordinate value than the point you are in now, for example, you are at Pi now, then you can only visit Pj(j < i). And in the end you back to P1 and the tour is over.
You should visit all points in this tour and you can visit every point only once.

Input
The input consists of multiple test cases. Each case begins with a line containing a positive integer n(2 <= n <= 200), means the number of points. Then following n lines each containing two positive integers Pi(xi, yi), indicating the coordinate of the i-th point in the plane.

Output
For each test case, output one line containing the shortest path to visit all the points with the rule mentioned above.The answer should accurate up to 2 decimal places.

Sample Input
3
1 1
2 3
3 1

Sample Output
6.47

Hint: The way 1 - 3 - 2 - 1 makes the shortest path.

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