leetcode_919. Complete Binary Tree Inserter_完全二叉树插入

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

给出树节点的定义和完全二叉树插入器类的定义，为这个类补全功能。完全二叉树的定义为：这颗二叉树除最后一层外左右层的节点都是满的(对于第i层有2^(i-1)个节点)，最后一层节点都出现在尽量靠左的位置。

 

/**
 * 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:
    CBTInserter(TreeNode* root) {}
    int insert(int v) {}
    TreeNode* get_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();

解法一：

我的思路是，先遍历给定二叉树，得到树的深度maxlayer和最后一层的节点数numoflastlayer。若numoflastlayer<2^(maxlayer-1)，则新节点插入在第layer=maxlayer层；若numoflastlayer=2^(maxlayer-1)，说明最后一层满了，需要插入到第layer=maxlayer+1层。再先序遍历这棵树，遍历到第layer-1层的节点时，判断：若节点只有左节点，则将新节点作为其右孩子；若节点无子节点，则将新节点作为其左孩子。

class CBTInserter
{
public:
    void preorder(TreeNode* root,int layer)
    {
        if(layer>maxlayer)
        {
            maxlayer = layer;
            numoflastlayer = 1;
        }
        else if(layer == maxlayer)
            numoflastlayer++;
        if(root->left!=NULL)
            preorder(root->left, layer+1);
        if(root->right!=NULL)
            preorder(root->right, layer+1);
    }
    CBTInserter(TreeNode* root)
    {
        root_ =root;
        maxlayer=-1;
        numoflastlayer=0;
        preorder(root,0);
    }

    TreeNode* Insert(TreeNode* root, int v, int layer, int insertlayer)
    {
        if(layer == insertlayer-1)
        {
            if(root->left == NULL)
            {
                root->left = new TreeNode(v);
                return root;
            }
            else if(root->right == NULL)
            {
                root->right = new TreeNode(v);
                return root;
            }
        }
        else
        {
            TreeNode* res = Insert(root->left, v, layer+1, insertlayer);
            if(res == NULL)
                res = Insert(root->right, v, layer+1, insertlayer);
            return res;
        }
        return NULL;
    }

    int insert(int v)
    {
        cout<<v<<endl;
        int maxnumoflastlayer = pow(2, maxlayer);
        TreeNode* res = NULL;
        if(numoflastlayer<maxnumoflastlayer)
        {
            res = Insert(root_,v,0, maxlayer);
            numoflastlayer++;
        }
        else
        {
            res = Insert(root_,v,0,maxlayer+1);
            maxlayer++;
            numoflastlayer=1;
        }
        return res->val;
    }

    TreeNode* get_root()
    {
        return root_;
    }
private:
    TreeNode* root_;
    int maxlayer;
    int numoflastlayer;
};

解法二：新节点插入的位置的父节点的子节点数要么为1，要么为0。根据层次遍历，把节点子节点数为0或1的节点存入队列。插入时，取队头节点，若该节点有左孩子，则将新节点作为其右孩子，并将该左右孩子压入队尾，将该队头节点出队；若该节点无孩子，则将新节点作为其左孩子，该节点仍然作为队头节点。

class CBTInserter
{
public:
    TreeNode* root_;
    queue<TreeNode*> nodes_0_1;
    CBTInserter(TreeNode* root)
    {
        root_ = root;
        queue<TreeNode*> que;
        que.push(root);
        while(!que.empty())
        {
            TreeNode* now = que.front();
            que.pop();
            if(now->left == NULL)
                nodes_0_1.push(now);
            else if(now->right == NULL)
                nodes_0_1.push(now);
            else
            {
                que.push(now->left);
                que.push(now->right);
            }
        }
    }

    int insert(int v)
    {
        TreeNode* root = nodes_0_1.front();
        if(root->left!=NULL)
        {
            root->right = new TreeNode(v);
            nodes_0_1.pop();
            nodes_0_1.push(root->left);
            nodes_0_1.push(root->right);
        }
        else
            root->left = new TreeNode(v);
        return root->val;
    }

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