问题 C: Simple Set Problem

Given $k$ non empty multiple sets, each multiple set only contains integers with absolute values not exceeding $10^9$.

It is required to select exactly one number from each multiple set to form an array (a1,a2,…,ak) with a length of $k$.

Assuming d=max(a1,a2,…,ak)−min(a1,a2,…,ak).Please calculate the minimum $d$.

Each test contains multiple test cases.The first line of input contains a single integer $t(1\le t\le 10^6)$---the number of test cases.The description of test cases follows.

The first line of each test case contains a single integer $k(1\le k\le 10^6)$ —— the number of multiple sets.

The following $k$ lines of each test case first read in a parameter ci —— indicating the size of the i-th multiple set, followed by ci integers with absolute values not exceeding $10^9$ —— indicating the elements of the $i$-th multiple set.

Guarantee that ∑i=1kci for each test case does not exceed 106106, the sum of ∑i=1kci for all test cases does not exceed $4\times 10^6$.

3
2
1 6
3 -7 7 10
4
9 -5 -9 2 8 5 4 3 3 8
2 10 8
1 -7
3 1 6 10
1
1 9

1
15
0