919. Complete Binary Tree Inserter

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919. Complete Binary Tree Inserter

Description

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.

Design an algorithm to insert a new node to a complete binary tree keeping it complete after the insertion.

Implement the CBTInserter class:

  • CBTInserter(TreeNode root) Initializes the data structure with the root of the complete binary tree.
  • int insert(int v) Inserts a TreeNode into the tree with value Node.val == val so that the tree remains complete, and returns the value of the parent of the inserted TreeNode.
  • TreeNode get_root() Returns the root node of the tree.

Example 1:

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Input

["CBTInserter", "insert", "insert", "get_root"]
[[[1, 2]], [3], [4], []]
Output

[null, 1, 2, [1, 2, 3, 4]]

Explanation

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

Constraints:

  • The number of nodes in the tree will be in the range [1, 1000].
  • 0 <= Node.val <= 5000
  • root is a complete binary tree.
  • 0 <= val <= 5000
  • At most 10^4 calls will be made to insert and get_root.

Hints/Notes

  • binary tree

Solution

Language: C++

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/**
 * 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:
    TreeNode* root_;
    queue<TreeNode*> q;

    CBTInserter(TreeNode* root) {
        root_ = root;
        q.push(root_);
        findParent();
    }

    int insert(int val) {
        TreeNode* cur = q.front();
        TreeNode* node = new TreeNode(val);
        if (!cur->left) {
            cur->left = node;
        } else if (!cur->right) {
            cur->right = node;
        }
        findParent();
        return cur->val;
    }

    TreeNode* get_root() { return root_; }

    void findParent() {
        TreeNode* cur = q.front();
        while (cur->left && cur->right) {
            q.push(cur->left);
            q.push(cur->right);
            q.pop();
            cur = q.front();
        }
    }
};

/**
 * 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();
 */