Choosing Cook Off Problems

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Dave is having trouble choosing problems for the upcoming cookoff.
The admins will be mad at him if he doesn't select problems with a gradually increasing level of difficulty.
To make his task easier, Dave has assigned a difficulty rating to each problem he has written.
A difficulty gap is defined as the absolute difference in difficulty rating between 2 problems,
where there is no other problem with a difficulty rating between them.
For example, if problems are chosen with difficulty ratings of 4, 7, 13, and 19, then the difficulty
gaps are 3, 6, and 6.
Dave has already chosen 2 problems for the cookoff,
and wants to choose the remaining problems in a way that minimizes the largest difficulty gap.
Input
Input begins with an integer T, the number of test cases.
Each test case begins with 4 integers N M C_{1} C_{2} on a line.
N is the number of problems to choose from (not including the two already chosen problems).
M is the number of problems that must be chosen (in addition to the two that have already been chosen).
C_{1} and C_{2} are the difficulty ratings of the 2 problems that have already been chosen.
Following this is a line with exactly N integers, giving the difficulty ratings of the remaining problems.
Again, the 2 already chosen problems are not included in the values of N and M.
A blank line separates each test case, including a blank line after the number of test cases.
Output
For each test case, output on a single line the minimum possible value of the largest difficulty gap.
Sample Input:
3 3 1 0 100 16 45 61 5 0 50 80 20 40 60 80 100 6 3 0 100 21 64 34 55 64 89
Sample Output:
55 30 34
Contsraints
T≤250
0≤M≤N≤1000
All difficulty ratings are between 0 and 1000000, inclusive.
Author:  pieguy 
Tester:  friggstad 
Editorial  http://discuss.codechef.com/problems/COOKOFF 
Tags  cook04, medium, pieguy 
Date Added:  9112010 
Time Limit:  0.75 sec 
Source Limit:  50000 Bytes 
Languages:  C, CPP14, JAVA, PYTH, PYTH 3.6, CS2, PAS fpc, PAS gpc, RUBY, PHP, GO, NODEJS, HASK, SCALA, D, PERL, FORT, WSPC, ADA, CAML, ICK, BF, ASM, CLPS, PRLG, ICON, SCM qobi, PIKE, ST, NICE, LUA, BASH, NEM, LISP sbcl, LISP clisp, SCM guile, JS, ERL, PERL6, TEXT, PYP3, CLOJ, FS 
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