A13759 | Boboniu and String

Boboniu defines BN-string as a string $s$ of characters 'B' and 'N'.

You can perform the following operations on the BN-string $s$ :

- Remove a character of $s$ .
- Remove a substring "BN" or "NB" of $s$ .
- Add a character 'B' or 'N' to the end of $s$ .
- Add a string "BN" or "NB" to the end of $s$ .

Note that a string $a$ is a substring of a string $b$ if $a$ can be obtained from $b$ by deletion of several (possibly, zero or all) characters from the beginning and several (possibly, zero or all) characters from the end.

Boboniu thinks that BN-strings $s$ and $t$ are similar if and only if:

- $|s|=|t|$ .
- There exists a permutation $p_1, p_2, \ldots, p_{|s|}$ such that for all $i$ ( $1\le i\le |s|$ ), $s_{p_i}=t_i$ .

Boboniu also defines $\text{dist}(s,t)$ , the distance between $s$ and $t$ , as the minimum number of operations that makes $s$ similar to $t$ .

Now Boboniu gives you $n$ non-empty BN-strings $s_1,s_2,\ldots, s_n$ and asks you to find a non-empty BN-string $t$ such that the maximum distance to string $s$ is minimized, i.e. you need to minimize $\max_{i=1}^n \text{dist}(s_i,t)$ .

The first line contains a single integer $n$ ( $1\le n\le 3\cdot 10^5$ ).

Each of the next $n$ lines contains a string $s_i$ ( $1\le |s_i| \le 5\cdot 10^5$ ). It is guaranteed that $s_i$ only contains 'B' and 'N'. The sum of $|s_i|$ does not exceed $5\cdot 10^5$ .

In the first line, print the minimum $\max_{i=1}^n \text{dist}(s_i,t)$ .

In the second line, print the suitable $t$ .

If there are several possible $t$ 's, you can print any.