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.

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

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]]

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

1. updating

class CBTInserter(object):
def __init__(self, root):
    self.deque = collections.deque()
    self.root = root
    q = collections.deque([root])
    while q:
        node = q.popleft()
        if not node.left or not node.right:
            self.deque.append(node)
        if node.left:
            q.append(node.left)
        if node.right:
            q.append(node.right)

def insert(self, v):
    node = self.deque[0]
    self.deque.append(TreeNode(v))
    if not node.left:
        node.left = self.deque[-1]
    else:
        node.right = self.deque[-1]
        self.deque.popleft()
    return node.val

def get_root(self):
    return self.root