
ZOJ Problem Set  1909
Given a set of sticks of various lengths, is it possible to join them endtoend to form a square?
The first line of input contains N, the number of test cases. Each test case begins with an integer 4 <= M <= 20, the number of sticks. M integers follow; each gives the length of a stick  an integer between 1 and 10,000.
For each case, output a line containing "yes" if is is possible to form a square; otherwise output "no".
Source: University of Waterloo Local Contest 2002.09.21 