对称轴（Symmetry, ACM / ICPC Seoul 2004 , UVa 1595） C语言写法

     The gure shown on the left is left-right symmetric as it is possible to fold the sheet of paper along a
vertical line, drawn as a dashed line, and to cut the gure into two identical halves. The gure on the
right is not left-right symmetric as it is impossible to nd such a vertical line.

       Write a program that determines whether a gure, drawn with dots, is left-right symmetric or not.
The dots are all distinct.

Input

The input consists of T test cases. The number of test cases T is given in the rst line of the input le.
The rst line of each test case contains an integer N, where N (1 N 1; 000) is the number of dots
in a gure. Each of the following N lines contains the x-coordinate and y-coordinate of a dot. Both
x-coordinat