CF1270G Subset with Zero Sum

You are given $ n $ integers $ a_1, a_2, \dots, a_n $ , such that for each $ 1\le i \le n $ holds $ i-n\le a_i\le i-1 $ . Find some nonempty subset of these integers, whose sum is equal to $ 0 $ . It can be shown that such a subset exists under given constraints. If there are several possible subsets with zero-sum, you can find any of them.

Each test contains multiple test cases. The first line contains the number of test cases $ t $ ( $ 1 \le t \le 10^6 $ ). The description of the test cases follows. The first line of each test case contains a single integer $ n $ ( $ 1\le n \le 10^6 $ ). The second line of each test case contains $ n $ integers $ a_1, a_2, \dots, a_n $ ( $ i-n \le a_i \le i-1 $ ). It is guaranteed that the sum of $ n $ over all test cases does not exceed $ 10^6 $ .

For each test case, output two lines. In the first line, output $ s $ ( $ 1\le s \le n $ ) — the number of elements in your subset. In the second line, output $ s $ integers $ i_1, i_2, \dots, i_s $ ( $ 1\le i_k \le n $ ). All integers have to be pairwise different, and $ a_{i_1} + a_{i_2} + \dots + a_{i_s} $ has to be equal to $ 0 $ . If there are several possible subsets with zero-sum, you can find any of them.

In the first example, we get sum is $ a_1 = 0 $ . In the second example, we get sum is $ a_1 + a_4 + a_3 + a_2 = 0 $ .