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| 1 | +using System; |
| 2 | +using System.Collections.Generic; |
| 3 | +using System.Linq; |
| 4 | +using System.Text; |
| 5 | + |
| 6 | +namespace Tree.TreeLib |
| 7 | +{ |
| 8 | + // // Given preorder and inorder traversal of a tree, construct the binary tree. |
| 9 | + |
| 10 | +// // Note: |
| 11 | +// // You may assume that duplicates do not exist in the tree. |
| 12 | + public class Solution |
| 13 | +{ |
| 14 | + private int[] _preorder; //preorder array |
| 15 | + private int[] _inorder; //inorder array |
| 16 | + public TreeNode BuildTree(int[] preorder, int[] inorder) |
| 17 | + { |
| 18 | + _preorder = preorder; |
| 19 | + _inorder = inorder; |
| 20 | + //if(_preorder.Length==0 || inorder.Length==0) return null; |
| 21 | + //if(prorder.Length!=inorder.Length) return null; |
| 22 | + return bulidTree(0,0,_inorder.Length-1); |
| 23 | + } |
| 24 | + //preStart: index of root of tree |
| 25 | + //inStart: of inorder tree, inStart ~ root index - 1 -> left tree |
| 26 | + //EndStart:of inorder tree, root index + 1 ~ inEnd -> right tree |
| 27 | + private TreeNode bulidTree(int preStart, int inStart, int inEnd) |
| 28 | + { |
| 29 | + if (preStart > _preorder.Length - 1 || inStart > inEnd) |
| 30 | + { |
| 31 | + return null; |
| 32 | + } |
| 33 | + TreeNode root = new TreeNode(_preorder[preStart]); |
| 34 | + // find the index of current root in inorder. |
| 35 | + int inIndex = curRootIndex(inStart, inEnd, root); |
| 36 | + root.left = bulidTree(preStart + 1, inStart, inIndex - 1); |
| 37 | + //right subtree begins position in preorder |
| 38 | + preStart += inIndex - inStart + 1; |
| 39 | + root.right = bulidTree(preStart, inIndex + 1, inEnd); |
| 40 | + return root; |
| 41 | + } |
| 42 | + |
| 43 | + private int curRootIndex(int inStart, int inEnd, TreeNode root) |
| 44 | + { |
| 45 | + for (int i = inStart; i <= inEnd; i++) |
| 46 | + { |
| 47 | + if (_inorder[i] == root.val) |
| 48 | + { |
| 49 | + return i; |
| 50 | + } |
| 51 | + } |
| 52 | + return -1; |
| 53 | + } |
| 54 | + |
| 55 | + } |
| 56 | + |
| 57 | +} |
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