A15430 | Equal Binary Subsequences

Everool has a binary string $s$ of length $2n$ . Note that a binary string is a string consisting of only characters $0$ and $1$ . He wants to partition $s$ into two disjoint equal subsequences. He needs your help to do it.

You are allowed to do the following operation exactly once.

- You can choose any subsequence (possibly empty) of $s$ and rotate it right by one position.

In other words, you can select a sequence of indices $b_1, b_2, \ldots, b_m$ , where $1 \le b_1 < b_2 < \ldots < b_m \le 2n$ . After that you simultaneously set $$$$s_{b_1} := s_{b_m}, $$ $$ s_{b_2} := s_{b_1}, $$ $$ \ldots, $$ $$ s_{b_m} := s_{b_{m-1}}. $$ </p><p>Can you partition $s$ into two <span class="tex-font-style-bf">disjoint equal</span> subsequences after performing the allowed operation <span class="tex-font-style-bf">exactly</span> once?</p><p>A partition of $s$ into two disjoint equal subsequences $s^p$ and $s^q$ is two <span class="tex-font-style-bf">increasing</span> arrays of indices $p\_1, p\_2, \\ldots, p\_n$ and $q\_1, q\_2, \\ldots, q\_n$ , such that each integer from $1$ to $2n$ is encountered in either $p$ or $q$ exactly once, $s^p = s\_{p\_1} s\_{p\_2} \\ldots s\_{p\_n}$ , $s^q = s\_{q\_1} s\_{q\_2} \\ldots s\_{q\_n}$ , and $s^p = s^q$ .</p><p>If it is not possible to partition after performing any kind of operation, report $-1$ . </p><p>If it is possible to do the operation and partition $s$ into two disjoint subsequences $s^p$ and $s^q$ , such that $s^p = s^q$ , print elements of $b$ and indices of $s^p$ , i. e. the values $p\_1, p\_2, \\ldots, p\_n$$$.

Each test contains multiple test cases. The first line contains the number of test cases $t$ ( $1 \le t \le 10^5$ ). Description of the test cases follows.

The first line of each test case contains a single integer $n$ ( $1 \le n \le 10^5$ ), where $2n$ is the length of the binary string.

The second line of each test case contains the binary string $s$ of length $2n$ .

It is guaranteed that the sum of $n$ over all test cases does not exceed $10^5$ .

For each test case, follow the following output format.

If there is no solution, print $-1$ .

Otherwise,

- In the first line, print an integer $m$ ( $0 \leq m \leq 2n$ ), followed by $m$ distinct indices $b_1$ , $b_2$ , ..., $b_m$ (in increasing order).
- In the second line, print $n$ distinct indices $p_1$ , $p_2$ , ..., $p_n$ (in increasing order).

If there are multiple solutions, print any.