Formatted question description: https://leetcode.ca/all/919.html

# 919. Complete Binary Tree Inserter (Medium)

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 = [[],,[]]
Output: [null,1,[1,2]]


Example 2:

Input: inputs = ["CBTInserter","insert","insert","get_root"], inputs = [[[1,2,3,4,5,6]],,,[]]
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.

Companies:

Related Topics:
Tree

## Solution 1.

// OJ: https://leetcode.com/problems/complete-binary-tree-inserter/

// Time:
//     CBTInserter: O(N)
//     insert: O(1)
//     get_root: O(1)
// Space: O(N)
class CBTInserter {
private:
TreeNode *root;
queue<TreeNode*> q;
public:
CBTInserter(TreeNode* root): root(root) {
if (!root) return;
queue<TreeNode*> tmp;
tmp.push(root);
while (tmp.size()) {
root = tmp.front();
tmp.pop();
if (!root->left || !root->right) q.push(root);
if (root->left) tmp.push(root->left);
if (root->right) tmp.push(root->right);
}
}

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

TreeNode* get_root() {
return root;
}
};