[C#]LeetCode919. 完全二叉树插入器 | Complete Binary Tree Inserter

A complete binary tree is a binary tree in which every level, except possibly the last, is completely filled, and all nodes are as far left as possible.

Write a data structure CBTInserter that is initialized with a complete binary tree and supports the following operations:

• CBTInserter(TreeNode root) initializes the data structure on a given tree with head node root;
• CBTInserter.insert(int v) will insert a TreeNode into the tree with value node.val = v so that the tree remains complete, and returns the value of the parent of the inserted TreeNode;
• CBTInserter.get_root() will return the head node of the tree.

Example 1:

Input: inputs = ["CBTInserter","insert","get_root"], inputs = [[[1]],[2],[]]
Output: [null,1,[1,2]]

Example 2:

Input: inputs = ["CBTInserter","insert","insert","get_root"], inputs = [[[1,2,3,4,5,6]],[7],[8],[]]
Output: [null,3,4,[1,2,3,4,5,6,7,8]]

Note:

1. The initial given tree is complete and contains between 1 and 1000 nodes.
2. CBTInserter.insert is called at most 10000 times per test case.
3. Every value of a given or inserted node is between 0 and 5000.

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完全二叉树是每一层（除最后一层外）都是完全填充（即，结点数达到最大）的，并且所有的结点都尽可能地集中在左侧。

设计一个用完全二叉树初始化的数据结构 CBTInserter，它支持以下几种操作：

• CBTInserter(TreeNode root) 使用头结点为 root 的给定树初始化该数据结构；
• CBTInserter.insert(int v) 将 TreeNode 插入到存在值为 node.val = v  的树中以使其保持完全二叉树的状态，并返回插入的 TreeNode 的父结点的值；
• CBTInserter.get_root() 将返回树的头结点。

示例 1：

输入：inputs = ["CBTInserter","insert","get_root"], inputs = [[[1]],[2],[]]
输出：[null,1,[1,2]]

示例 2：

输入：inputs = ["CBTInserter","insert","insert","get_root"], inputs = [[[1,2,3,4,5,6]],[7],[8],[]]
输出：[null,3,4,[1,2,3,4,5,6,7,8]]

提示：

1. 最初给定的树是完全二叉树，且包含 1 到 1000 个结点。
2. 每个测试用例最多调用 CBTInserter.insert  操作 10000 次。
3. 给定结点或插入结点的每个值都在 0 到 5000 之间。

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 1 /**
 2  * Definition for a binary tree node.
 3  * public class TreeNode {
 4  *     int val;
 5  *     TreeNode left;
 6  *     TreeNode right;
 7  *     TreeNode(int x) { val = x; }
 8  * }
 9  */
10 class CBTInserter {
11     TreeNode root;
12     int cnt;
13     private int calc(TreeNode root) {
14         if (root == null) {
15             return 0;
16         }
17         return calc(root.left) + calc(root.right) + 1;
18     }
19     public CBTInserter(TreeNode root) {
20         this.root = root;
21         cnt = calc(root);
22     }
23     
24     public int insert(int v) {
25         int cur = ++cnt;
26         int ipos = 31;
27         while ((cur & (1 << ipos)) == 0) {
28             ipos--;
29         }
30         ipos--;
31         TreeNode curNode = root;
32         while (ipos > 0) {
33             if ((cur & (1 << ipos)) == 0) {
34                 curNode = curNode.left;
35             } else {
36                 curNode = curNode.right;
37             }
38             ipos--;
39         }
40         if ((cur & (1 << ipos)) == 0) {
41             curNode.left = new TreeNode(v);
42         } else {
43             curNode.right = new TreeNode(v);
44         }
45         return curNode.val;
46     }
47     
48     public TreeNode get_root() {
49         return root;
50     }
51 }
52 
53 /**
54  * Your CBTInserter object will be instantiated and called as such:
55  * CBTInserter obj = new CBTInserter(root);
56  * int param_1 = obj.insert(v);
57  * TreeNode param_2 = obj.get_root();
58  */