"Leetcode-Interview algorithm classic-java implementation" "106-construct binary tree from Inorder and postorder traversal (construction of two Fork Trees II)"

Source: Internet
Author: User

"106-construct binary tree from Inorder and postorder traversal (construct two-fork trees via middle order and post-sequence traversal)" "leetcode-Interview algorithm classic-java Implementation" "All Topics folder Index" Original Question

Given Inorder and Postorder traversal of a tree, construct the binary tree.
  Note:
Assume that duplicates does not exist in the tree.

Main Topic

A binary tree is constructed, given a sequence traversal and sequential traversal sequences.
  Note:
There are no repeating elements in the tree

Thinking of solving problems

The last element of the post-order traversal is the root node (value R) of the tree, where the value of R is found in the sequential traversal sequence IDX,IDX the sequence traversal sequences into the left and right two subtrees, which can be divided into two sub-trees by the sequential traversal sequence. It is solved by recursion.

Code Implementation

publicclass TreeNode {    int val;    TreeNode left;    TreeNode right;    TreeNode(int x) { val = x; }}

Algorithm implementation class

 Public  class solution {     PublicTreeNodeBuildtree(int[] inorder,int[] postorder) {//test of the parameters        if(Inorder = =NULL|| Postorder = =NULL|| Inorder.length = =0|| Inorder.length! = postorder.length) {return NULL; }//Build a binary tree        returnSolve (Inorder,0, Inorder.length-1, Postorder,0, Postorder.length-1); }/** * Build binary Tree * * @param inorder Results of sequential traversal * @param x start position of the sequence traversal * @par the end position of the sequence traversal in am y * @param postorder Results of post-order traversal * @param The start position of the sequential traversal * @p Aram J post-traversal end position * @return two fork tree * /     PublicTreeNodeSolve(int[] inorder,intXintYint[] Postorder,intIintj) {if(x >=0&& x <= y && i >=0&& I <= j) {//There is only one element, (at this time there is also i=j)            if(x = = y) {return NewTreeNode (Postorder[j]); }//More than one element. There are also i<j at this time            Else if(x < y) {//Create root nodeTreeNode root =NewTreeNode (Postorder[j]);//Find root node subscript in middle sequence traversal                intIDX = x; while(Idx < y && inorder[idx]! = Postorder[j])                {idx++; }//Left dial hand tree non-empty, build left sub-tree                intLeftlength = Idx-x;if(Leftlength >0) {//I, I + leftLength-1, start of the left subtree of the pre-sequence traversal, end positionRoot.left = Solve (inorder, X, IDX-1, Postorder, I, i + leftlength-1); }//Right subtree non-empty, build right sub-tree                intRightlength = Y-idx;if(Rightlength >0) {//i + Leftlength, j-1, start of the right subtree of the pre-sequence traversal, end positionRoot.right = Solve (inorder, IDX +1, Y, Postorder, i + leftlength, J-1); }returnRoot }Else{return NULL; }        }return NULL; }}
Assessment Results

  Click on the picture, the mouse does not release. Drag a position to view the full picture in the new form after you release it.

Special Instructions Welcome reprint, Reprint please indicate the source "http://blog.csdn.net/derrantcm/article/details/47371993"

"Leetcode-Interview algorithm classic-java implementation" "106-construct binary tree from Inorder and postorder traversal (construction of two Fork Trees II)"

Contact Us

The content source of this page is from Internet, which doesn't represent Alibaba Cloud's opinion; products and services mentioned on that page don't have any relationship with Alibaba Cloud. If the content of the page makes you feel confusing, please write us an email, we will handle the problem within 5 days after receiving your email.

If you find any instances of plagiarism from the community, please send an email to: info-contact@alibabacloud.com and provide relevant evidence. A staff member will contact you within 5 working days.

A Free Trial That Lets You Build Big!

Start building with 50+ products and up to 12 months usage for Elastic Compute Service

  • Sales Support

    1 on 1 presale consultation

  • After-Sales Support

    24/7 Technical Support 6 Free Tickets per Quarter Faster Response

  • Alibaba Cloud offers highly flexible support services tailored to meet your exact needs.