Encode N ary Tree to Binary Tree

This page explains Java solution to problem Encode N ary Tree to Binary Tree using Tree data structure.

Problem Statement

Design an algorithm to encode an N-ary tree into a binary tree and decode the binary tree to get the original N-ary tree.

An N-ary tree is a rooted tree in which each node has no more than N children. Similarly, a binary tree is a rooted tree in which each node has no more than 2 children.

There is no restriction on how your encode/decode algorithm should work.

Solution

package com.vc.hard;

import java.util.ArrayList;

/**
// Definition for a Node.
class Node {
    public int val;
    public List<Node> children;

    public Node() {}

    public Node(int _val) {
        val = _val;
    }

    public Node(int _val, List<Node> _children) {
        val = _val;
        children = _children;
    }
};
*/

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */

class EncodeNAryTreeToBinaryTree {

    // Encodes an n-ary tree to a binary tree.
    public TreeNode encode(Node root) {
        if(root == null) return null;
        else {
            TreeNode tree = new TreeNode(root.val);
            if(root.children != null && root.children.size() > 0) {
                tree.left = encode(root.children.get(0));
                TreeNode current = tree.left;
                for(int i = 1; i < root.children.size(); i++) {
                    current.right = encode(root.children.get(i));
                    current = current.right;
                }
            }
            return tree;
        }
    }

    // Decodes your binary tree to an n-ary tree.
    public Node decode(TreeNode root) {
        if(root == null) return null;
        else {
            Node node = new Node(root.val, new ArrayList<>());
            TreeNode current = root.left;
            while(current != null) {
                node.children.add(decode(current));
                current = current.right;
            }
            return node;
        }
    }
}

Time Complexity

O(N) Where
N is total number of elements in an input tree

Space Complexity

O(1)