• Leetcode: Construct Binary Tree from Inorder and Postorder Traversal


    Given inorder and postorder traversal of a tree, construct the binary tree.

    Construct Binary Tree from Inorder and Preorder Traversal问题非常类似,唯一区别在于这一次确定root的位置由post traversal来确定,为最后一个元素。

     1 /**
     2  * Definition for binary tree
     3  * public class TreeNode {
     4  *     int val;
     5  *     TreeNode left;
     6  *     TreeNode right;
     7  *     TreeNode(int x) { val = x; }
     8  * }
     9  */
    10 public class Solution {
    11     public TreeNode buildTree(int[] inorder, int[] postorder) {
    12         if (inorder.length==0 || postorder.length==0 || inorder.length!=postorder.length) {
    13             return null;
    14         }
    15         int len = inorder.length;
    16         HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
    17         for (int i=0; i<inorder.length; i++) {
    18             map.put(inorder[i], i);
    19         }
    20         return helper(postorder, 0, len-1, inorder, 0, len-1, map);
    21     }
    22     
    23     public TreeNode helper(int[] postorder, int posL, int posR, int[] inorder, int inL, int inR, HashMap<Integer, Integer> map) {
    24         if (posL>posR || inL>inR) {
    25             return null;
    26         }
    27         TreeNode root = new TreeNode(postorder[posR]);
    28         int index = map.get(postorder[posR]);
    29         root.left = helper(postorder, posL, posL+index-1-inL, inorder, inL, index-1, map);
    30         root.right = helper(postorder, posL+index-inL, posR-1, inorder, index+1, inR, map);
    31         return root;
    32     }
    33 }
  • 相关阅读:
    工具类官网Web原型制作分享-Adobe
    还在为黑白网页设计犯难?12款设计帮你轻松解决!!!
    联系我们吧
    单调栈&&单调队列
    *模板--数据结构
    非递归线段树专题
    反素数
    线段树专题训练
    BST
    排列与组合
  • 原文地址:https://www.cnblogs.com/EdwardLiu/p/3974452.html
Copyright © 2020-2023  润新知