package DataStructures.Trees;

import java.util.HashMap;
import java.util.Map;
import DataStructures.Trees.BinaryTree.Node;

/**
 * Approach: Naive Solution: Create root node from first value present in
 * preorder traversal. Look for the index of root node's value in inorder
 * traversal. That will tell total nodes present in left subtree and right
 * subtree. Based on that index create left and right subtree.
 * Complexity:
 * Time: O(n^2) for each node there is iteration to find index in inorder array
 * Space: Stack size = O(height) = O(lg(n))
 *
 * Optimized Solution: Instead of iterating over inorder array to find index of
 * root value, create a hashmap and find out the index of root value.
 * Complexity:
 * Time: O(n) hashmap reduced iteration to find index in inorder array
 * Space: O(n) space taken by hashmap
 *
 */
public class CreateBinaryTreeFromInorderPreorder {
 public static void main(String[] args) {
 test(new Integer[] {}, new Integer[] {}); // empty tree
 test(new Integer[] { 1 }, new Integer[] { 1 }); // single node tree
 test(new Integer[] { 1, 2, 3, 4 }, new Integer[] { 1, 2, 3, 4 }); // right skewed tree
 test(new Integer[] { 1, 2, 3, 4 }, new Integer[] { 4, 3, 2, 1 }); // left skewed tree
 test(new Integer[] { 3, 9, 20, 15, 7 }, new Integer[] { 9, 3, 15, 20, 7 }); // normal tree
 }

 private static void test(final Integer[] preorder, final Integer[] inorder) {
 System.out.println("\n====================================================");
 System.out.println("Naive Solution...");
 BinaryTree root = new BinaryTree(createTree(preorder, inorder, 0, 0, inorder.length));
 System.out.println("Preorder Traversal: ");
 root.preOrder(root.getRoot());
 System.out.println("\nInorder Traversal: ");
 root.inOrder(root.getRoot());
 System.out.println("\nPostOrder Traversal: ");
 root.postOrder(root.getRoot());

 Map<Integer, Integer> map = new HashMap<>();
 for (int i = 0; i < inorder.length; i++) {
 map.put(inorder[i], i);
 }
 BinaryTree optimizedRoot = new BinaryTree(createTreeOptimized(preorder, inorder, 0, 0, inorder.length, map));
 System.out.println("\n\nOptimized solution...");
 System.out.println("Preorder Traversal: ");
 optimizedRoot.preOrder(root.getRoot());
 System.out.println("\nInorder Traversal: ");
 optimizedRoot.inOrder(root.getRoot());
 System.out.println("\nPostOrder Traversal: ");
 optimizedRoot.postOrder(root.getRoot());
 }

 private static Node createTree(final Integer[] preorder, final Integer[] inorder,
 final int preStart, final int inStart, final int size) {
 if (size == 0) {
 return null;
 }

 Node root = new Node(preorder[preStart]);
 int i = inStart;
 while (preorder[preStart] != inorder[i]) {
 i++;
 }
 int leftNodesCount = i - inStart;
 int rightNodesCount = size - leftNodesCount - 1;
 root.left = createTree(preorder, inorder, preStart + 1, inStart, leftNodesCount);
 root.right = createTree(preorder, inorder, preStart + leftNodesCount + 1, i + 1,
 rightNodesCount);
 return root;

 }

 private static Node createTreeOptimized(final Integer[] preorder, final Integer[] inorder,
 final int preStart, final int inStart, final int size,
 final Map<Integer, Integer> inorderMap) {
 if (size == 0) {
 return null;
 }

 Node root = new Node(preorder[preStart]);
 int i = inorderMap.get(preorder[preStart]);
 int leftNodesCount = i - inStart;
 int rightNodesCount = size - leftNodesCount - 1;
 root.left = createTreeOptimized(preorder, inorder, preStart + 1, inStart,
 leftNodesCount, inorderMap);
 root.right = createTreeOptimized(preorder, inorder, preStart + leftNodesCount + 1,
 i + 1, rightNodesCount, inorderMap);
 return root;
 }

}