0919.Complete Binary Tree Inserter

919. 完全二叉树插入器

English Version

题目描述

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

设计一种算法，将一个新节点插入到一个完整的二叉树中，并在插入后保持其完整。

实现 CBTInserter 类:

• CBTInserter(TreeNode root) 使用头节点为 root 的给定树初始化该数据结构；
• CBTInserter.insert(int v)  向树中插入一个值为 Node.val == val的新节点 TreeNode。使树保持完全二叉树的状态，并返回插入节点 TreeNode 的父节点的值；
• CBTInserter.get_root() 将返回树的头节点。

 

示例 1：

输入
["CBTInserter", "insert", "insert", "get_root"]
[[[1, 2]], [3], [4], []]
输出
[null, 1, 2, [1, 2, 3, 4]]

解释
CBTInserter cBTInserter = new CBTInserter([1, 2]);
cBTInserter.insert(3);  // 返回 1
cBTInserter.insert(4);  // 返回 2
cBTInserter.get_root(); // 返回 [1, 2, 3, 4]

 

提示：

• 树中节点数量范围为 [1, 1000] 
• 0 <= Node.val <= 5000
• root 是完全二叉树
• 0 <= val <= 5000 
• 每个测试用例最多调用 insert 和 get_root 操作 104 次

解法

Python3

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class CBTInserter:

    def __init__(self, root: TreeNode):
        self.tree = []
        q = deque([root])
        while q:
            n = len(q)
            for _ in range(n):
                node = q.popleft()
                self.tree.append(node)
                if node.left:
                    q.append(node.left)
                if node.right:
                    q.append(node.right)

    def insert(self, val: int) -> int:
        pidx = (len(self.tree) - 1) >> 1
        node = TreeNode(val=val)
        self.tree.append(node)
        if self.tree[pidx].left is None:
            self.tree[pidx].left = node
        else:
            self.tree[pidx].right = node
        return self.tree[pidx].val

    def get_root(self) -> TreeNode:
        return self.tree[0]


# Your CBTInserter object will be instantiated and called as such:
# obj = CBTInserter(root)
# param_1 = obj.insert(val)
# param_2 = obj.get_root()

Java

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class CBTInserter {
    private List<TreeNode> tree;

    public CBTInserter(TreeNode root) {
        tree = new ArrayList<>();
        Deque<TreeNode> q = new ArrayDeque<>();
        q.offerLast(root);
        while (!q.isEmpty()) {
            TreeNode node = q.pollFirst();
            tree.add(node);
            if (node.left != null) {
                q.offerLast(node.left);
            }
            if (node.right != null) {
                q.offerLast(node.right);
            }
        }
    }

    public int insert(int val) {
        int pidx = (tree.size() - 1) >> 1;
        TreeNode node = new TreeNode(val);
        tree.add(node);
        if (tree.get(pidx).left == null) {
            tree.get(pidx).left = node;
        } else {
            tree.get(pidx).right = node;
        }
        return tree.get(pidx).val;
    }

    public TreeNode get_root() {
        return tree.get(0);
    }
}

/**
 * Your CBTInserter object will be instantiated and called as such:
 * CBTInserter obj = new CBTInserter(root);
 * int param_1 = obj.insert(val);
 * TreeNode param_2 = obj.get_root();
 */

C++

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class CBTInserter {
public:
    vector<TreeNode*> tree;

    CBTInserter(TreeNode* root) {
        queue<TreeNode*> q;
        q.push(root);
        while (!q.empty())
        {
            auto node = q.front();
            q.pop();
            tree.push_back(node);
            if (node->left) q.push(node->left);
            if (node->right) q.push(node->right);
        }
    }

    int insert(int val) {
        int pidx = tree.size() - 1 >> 1;
        TreeNode* node = new TreeNode(val);
        tree.push_back(node);
        if (!tree[pidx]->left) tree[pidx]->left = node;
        else tree[pidx]->right = node;
        return tree[pidx]->val;
    }

    TreeNode* get_root() {
        return tree[0];
    }
};

/**
 * Your CBTInserter object will be instantiated and called as such:
 * CBTInserter* obj = new CBTInserter(root);
 * int param_1 = obj->insert(val);
 * TreeNode* param_2 = obj->get_root();
 */

Go

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
type CBTInserter struct {
	tree []*TreeNode
}

func Constructor(root *TreeNode) CBTInserter {
	var q []*TreeNode
	var tree []*TreeNode
	q = append(q, root)
	for len(q) > 0 {
		node := q[0]
		tree = append(tree, node)
		q = q[1:]
		if node.Left != nil {
			q = append(q, node.Left)
		}
		if node.Right != nil {
			q = append(q, node.Right)
		}
	}
	return CBTInserter{tree}
}

func (this *CBTInserter) Insert(val int) int {
	pidx := (len(this.tree) - 1) >> 1
	node := &TreeNode{Val: val}
	this.tree = append(this.tree, node)
	if this.tree[pidx].Left == nil {
		this.tree[pidx].Left = node
	} else {
		this.tree[pidx].Right = node
	}
	return this.tree[pidx].Val
}

func (this *CBTInserter) Get_root() *TreeNode {
	return this.tree[0]
}

/**
 * Your CBTInserter object will be instantiated and called as such:
 * obj := Constructor(root);
 * param_1 := obj.Insert(val);
 * param_2 := obj.Get_root();
 */

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