Problem:
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Reconstruction of a Tree

Write a program which reads two sequences of nodes obtained by the preorder tree walk and the inorder tree walk on a binary tree respectively, and prints a sequence of the nodes obtained by the postorder tree walk on the binary tree.

Input

In the first line, an integer $n$, which is the number of nodes in the binary tree, is given.

In the second line, the sequence of node IDs obtained by the preorder tree walk is given separated by space characters.

In the second line, the sequence of node IDs obtained by the inorder tree walk is given separated by space characters.

Every node has a unique ID from $1$ to $n$. Note that the root does not always correspond to $1$.

Output

Print the sequence of node IDs obtained by the postorder tree walk in a line. Put a single space character between adjacent IDs.

Constraints

$1 \leq n \leq 40$

Sample Input 1

5
1 2 3 4 5
3 2 4 1 5

Sample Output 1

3 4 2 5 1

Sample Input 2

4
1 2 3 4
1 2 3 4

Sample Output 2

4 3 2 1

Solution in C# (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace COJ1_7
{
    struct Node
    {
        public int value;
        public int left;
        public int right;
    }
    class Program
    {

        static void Main(string[] args)
        {
            int cnt = int.Parse(Console.ReadLine());
            Node[] nodes = new Node[cnt];
            for (int i = 0; i < cnt; i++)
            {
                nodes[i].left = -1;
                nodes[i].right = -1;
            }
            var preorder = Array.ConvertAll(Console.ReadLine().Split(' '), int.Parse);
            var inorder = Array.ConvertAll(Console.ReadLine().Split(' '), int.Parse);

            GetTree(nodes, preorder, inorder, 0, cnt, 0);
            StringBuilder builder = new StringBuilder();
            PostOrder(builder, nodes, 0);
            Console.WriteLine(builder.ToString());
        }

        public static void GetTree(Node[] nodes, int[] preorder, int[] inorder, int from, int to, int index)
        {
            int value = preorder[index];
            nodes[index].value = value;
            int sep = from;
            for (int i = from; i < to; i++)
            {
                if (inorder[i] == value) sep = i;
            }
            if (sep != from)
            {
                nodes[index].left = index + 1;
                GetTree(nodes, preorder, inorder, from, sep, index + 1);
            }
            if (sep < to-1)
            {
                int gap = sep - from;
                nodes[index].right = index + 1 + gap;
                GetTree(nodes, preorder, inorder, sep + 1, to, index + gap + 1);
            }
            return;
        }
        public static void PostOrder(StringBuilder builder, Node[] nodes, int index)
        {
            if (nodes[index].left != -1)
                PostOrder(builder, nodes, nodes[index].left);
            if (nodes[index].right != -1)
                PostOrder(builder, nodes, nodes[index].right);
            if (index == 0)
                builder.Append(nodes[index].value);
            else builder.Append(nodes[index].value).Append(" ");
        }
    }
}