AB Tree

2000ms

262144K

Description:

Kilani and Abd are neighbors for 3000 years, but then the day came and Kilani decided to move to another house. As a farewell gift, Kilani is going to challenge Abd with a problem written by their other neighbor with the same name Abd.

$\text{[math]}$

The problem is:

You are given a connected tree rooted at node $$$1$$$.

You should assign a character a or b to every node in the tree so that the total number of a's is equal to $$$x$$$ and the total number of b's is equal to $$$n - x$$$.

Let's define a string for each node $$$v$$$ of the tree as follows:

if $$$v$$$ is root then the string is just one character assigned to $$$v$$$:
otherwise, let's take a string defined for the $$$v$$$'s parent $$$p_v$$$ and add to the end of it a character assigned to $$$v$$$.

You should assign every node a character in a way that minimizes the number of distinct strings among the strings of all nodes.

Input:

The first line contains two integers $$$n$$$ and $$$x$$$ ($$$1 \leq n \leq 10^5$$$; $$$0 \leq x \leq n$$$) — the number of vertices in the tree the number of a's.

The second line contains $$$n - 1$$$ integers $$$p_2, p_3, \dots, p_{n}$$$ ($$$1 \leq p_i \leq n$$$; $$$p_i \neq i$$$), where $$$p_i$$$ is the parent of node $$$i$$$.

It is guaranteed that the input describes a connected tree.

Output:

In the first line, print the minimum possible total number of distinct strings.

In the second line, print $$$n$$$ characters, where all characters are either a or b and the $$$i$$$-th character is the character assigned to the $$$i$$$-th node.

Make sure that the total number of a's is equal to $$$x$$$ and the total number of b's is equal to $$$n - x$$$.

If there is more than one answer you can print any of them.