919. 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]]

 1 class CBTInserter {
 2     private TreeNode root;
 3 
 4     public CBTInserter(TreeNode root) {
 5         this.root = root;
 6     }
 7 
 8     public int insert(int v) {
 9         Queue<TreeNode> q = new LinkedList<>();
10         q.offer(root);
11         while (!q.isEmpty()) {
12             TreeNode n = q.poll();
13             if (n.right != null) { // n has 2 children.
14                 q.offer(n.left);
15                 q.offer(n.right);
16             } else {
17                 if (n.left == null) {
18                     n.left = new TreeNode(v);
19                 } else {
20                     n.right = new TreeNode(v);
21                 }
22                 return n.val;
23             }
24         }
25         return -1;
26     }
27 
28     public TreeNode get_root() {
29         return root;
30     }
31 }

还有一种方法是把没有两个children的node单独放在一个queue里面，这样每次添加的时候，从queue的head取就知道那个是parent. 

 1 class CBTInserter {
 2     private TreeNode root;
 3     private Queue<TreeNode> nodesWithNullChild;
 4 
 5     public CBTInserter(TreeNode root) {
 6         this.root = root;
 7         this.nodesWithNullChild = new LinkedList<>();
 8         Queue<TreeNode> q = new LinkedList<>();
 9         q.offer(root);
10         while (!q.isEmpty()) {
11             TreeNode n = q.poll();
12             if (n.left == null || n.right == null) { 
13                 nodesWithNullChild.offer(n);
14             } 
15             if (n.left != null) {
16                     q.offer(n.left);
17             } 
18             if (n.right != null) {
19                     q.offer(n.right);
20             }
21         }
22     }
23 
24     public int insert(int v) {
25         TreeNode newNode = new TreeNode(v);
26         TreeNode firstNode = nodesWithNullChild.peek();
27         if (firstNode.left == null) {
28             firstNode.left = newNode;
29         } else {
30             firstNode.right = newNode;
31             nodesWithNullChild.poll();
32         }
33         nodesWithNullChild.offer(newNode);
34         return firstNode.val;
35     }
36 
37     public TreeNode get_root() {
38         return root;
39     }
40 }

 

posted @ 2021-03-13 08:13  北叶青藤  阅读(47)  评论(0)    收藏  举报