CF1927B Following the String

Polycarp lost the string $ s $ of length $ n $ consisting of lowercase Latin letters, but he still has its trace. The trace of the string $ s $ is an array $ a $ of $ n $ integers, where $ a_i $ is the number of such indices $ j $ ( $ j < i $ ) that $ s_i=s_j $ . For example, the trace of the string abracadabra is the array \[ $ 0, 0, 0, 1, 0, 2, 0, 3, 1, 1, 4 $ \]. Given a trace of a string, find any string $ s $ from which it could have been obtained. The string $ s $ should consist only of lowercase Latin letters a-z.

The first line of the input contains a single integer $ t $ ( $ 1 \le t \le 10^4 $ ) — the number of test cases. Then the descriptions of the test cases follow. The first line of each test case contains a single integer $ n $ ( $ 1 \le n \le 2 \cdot 10^5 $ ) — the length of the lost string. The second line of each test case contains $ n $ integers $ a_1, a_2, \dots, a_n $ ( $ 0 \le a_i < n $ ) — the trace of the string. It is guaranteed that for the given trace, there exists a suitable string $ s $ . It is guaranteed that the sum of $ n $ over all test cases does not exceed $ 2 \cdot 10^5 $ .

For each test case, output a string $ s $ that corresponds to the given trace. If there are multiple such strings $ s $ , then output any of them. The string $ s $ should consist of lowercase Latin letters a-z. It is guaranteed that for each test case, a valid answer exists.