919. Complete Binary Tree Inserter（python+cpp）

题目：

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 treeremains 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]]  

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

解释：
完全二叉树，需要用层序遍历做。
python代码：

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

class CBTInserter(object):

    def __init__(self, root):
        """
        :type root: TreeNode
        """
        self.root=root
        #层序遍历找到父节点
        self.queue=[]
        self.queue.append(root)
        while True:
            front=self.queue[0]
            if not front.left:
                break
            self.queue.append(front.left)
            if not front.right:
                break
            self.queue.append(front.right)
            self.queue.pop(0)
        
    def insert(self, v):
        """
        :type v: int
        :rtype: int
        """
        tmpnode=TreeNode(v)
        parent=self.queue[0]
        if not parent.left:
            parent.left=tmpnode
        else:
            parent.right=tmpnode
            self.queue.pop(0)
        self.queue.append(tmpnode)
        return parent.val
        
    def get_root(self):
        """
        :rtype: TreeNode
        """
        return self.root
        
# Your CBTInserter object will be instantiated and called as such:
# obj = CBTInserter(root)
# param_1 = obj.insert(v)
# param_2 = obj.get_root()

c++代码：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class CBTInserter {
public:
    TreeNode* global_root;
    queue<TreeNode*> _queue;
    CBTInserter(TreeNode* root) {
        global_root=root;
        _queue.push(root);
        while(true)
        {
            TreeNode* tmp=_queue.front();
            if(! tmp->left)
                break;
            _queue.push(tmp->left);
            if(!tmp->right)
                break;
            _queue.push(tmp->right);
            _queue.pop();
        }
    }
    
    int insert(int v) {
        TreeNode* parent=_queue.front();
        TreeNode* tmpNode=new TreeNode(v);
        if(!parent->left)
            parent->left=tmpNode;
        else
        {
            parent->right=tmpNode;
            _queue.pop();
        }
        _queue.push(tmpNode);
        return parent->val;
    }
    
    TreeNode* get_root() {
        return global_root;
    }
};

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

总结：