| | | 1 | | // -------------------------------------------------------------------------------- |
| | | 2 | | // Copyright (C) 2025 Eugene Eremeev (also known as Yevhenii Yeriemeieiv). |
| | | 3 | | // All Rights Reserved. |
| | | 4 | | // -------------------------------------------------------------------------------- |
| | | 5 | | // This software is the confidential and proprietary information of Eugene Eremeev |
| | | 6 | | // (also known as Yevhenii Yeriemeieiv) ("Confidential Information"). You shall not |
| | | 7 | | // disclose such Confidential Information and shall use it only in accordance with |
| | | 8 | | // the terms of the license agreement you entered into with Eugene Eremeev (also |
| | | 9 | | // known as Yevhenii Yeriemeieiv). |
| | | 10 | | // -------------------------------------------------------------------------------- |
| | | 11 | | |
| | | 12 | | using LeetCode.Core.Models; |
| | | 13 | | |
| | | 14 | | namespace LeetCode.Algorithms.ConstructBinaryTreeFromPreorderAndPostorderTraversal; |
| | | 15 | | |
| | | 16 | | /// <inheritdoc /> |
| | | 17 | | public class ConstructBinaryTreeFromPreorderAndPostorderTraversalRecursive : |
| | | 18 | | IConstructBinaryTreeFromPreorderAndPostorderTraversal |
| | | 19 | | { |
| | | 20 | | /// <summary> |
| | | 21 | | /// Time complexity - O(n) |
| | | 22 | | /// Space complexity - O(n) |
| | | 23 | | /// </summary> |
| | | 24 | | /// <param name="preorder"></param> |
| | | 25 | | /// <param name="postorder"></param> |
| | | 26 | | /// <returns></returns> |
| | | 27 | | public TreeNode ConstructFromPrePost(int[] preorder, int[] postorder) |
| | 2 | 28 | | { |
| | 2 | 29 | | return ConstructFromPrePost(preorder, postorder, 0, preorder.Length - 1, 0)!; |
| | 2 | 30 | | } |
| | | 31 | | |
| | | 32 | | private static TreeNode? ConstructFromPrePost(int[] preorder, int[] postorder, int preorderStart, int preorderEnd, |
| | | 33 | | int postorderStart) |
| | 8 | 34 | | { |
| | 8 | 35 | | if (preorderStart > preorderEnd) |
| | 0 | 36 | | { |
| | 0 | 37 | | return null; |
| | | 38 | | } |
| | | 39 | | |
| | 8 | 40 | | if (preorderStart == preorderEnd) |
| | 5 | 41 | | { |
| | 5 | 42 | | return new TreeNode(preorder[preorderStart]); |
| | | 43 | | } |
| | | 44 | | |
| | 3 | 45 | | var numOfNodesInLeft = 1; |
| | | 46 | | |
| | 5 | 47 | | while (postorder[postorderStart + numOfNodesInLeft - 1] != preorder[preorderStart + 1]) |
| | 2 | 48 | | { |
| | 2 | 49 | | numOfNodesInLeft++; |
| | 2 | 50 | | } |
| | | 51 | | |
| | 3 | 52 | | var left = ConstructFromPrePost(preorder, postorder, preorderStart + 1, preorderStart + numOfNodesInLeft, |
| | 3 | 53 | | postorderStart); |
| | | 54 | | |
| | 3 | 55 | | var right = ConstructFromPrePost(preorder, postorder, preorderStart + numOfNodesInLeft + 1, preorderEnd, |
| | 3 | 56 | | postorderStart + numOfNodesInLeft); |
| | | 57 | | |
| | 3 | 58 | | return new TreeNode(preorder[preorderStart], left, right); |
| | 8 | 59 | | } |
| | | 60 | | } |