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.

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]]

树的广度优先搜索(利用队列实现）+ 完全二叉树父节点和子节点的下标索引关系

class CBTInserter {
    TreeNode *root{nullptr};
    vector<TreeNode *> nodes;
    void bfs(TreeNode* root){
        queue<TreeNode*> qu;
        if(root) qu.push(root);
        while(!qu.empty()){
            TreeNode* parent=qu.front();
            nodes.push_back(parent);
            qu.pop();
            if(parent->left)
                qu.push(parent->left);
            if(parent->right)
                qu.push(parent->right);
        }
    }

public:
    CBTInserter(TreeNode *root) {
        this->root = root;
        bfs(root);
    }

    int insert(int v) {
        TreeNode *node = new TreeNode(v);
        nodes.push_back(node);
        int sz=nodes.size();
        TreeNode* parent=nodes[sz/2-1];
        cout<<"parent idx: "<<sz/2-1<<endl;
        if(sz%2==0)
            parent->left=node;
        else
            parent->right=node;
//        if(sz==1) return 0;   测试用例没有考虑构造函数调用为 CBTInserter(nullptr) 的情况
        return parent->val;
    }

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

去掉queue

class CBTInserter {
    TreeNode *root{nullptr};
    vector<TreeNode *> nodes;
    void bfs(TreeNode* root){
        if(root==nullptr) return;
        nodes.push_back(root);
        int i=0;//i表示当前父节点的索引
        int sz=1;//s表示当前向量nodes的长度
        while(i<sz){
            TreeNode* parent=nodes[i];
            if(parent->left){
                nodes.push_back(parent->left);
                sz+=1;
            }
            if(parent->right){
                nodes.push_back(parent->right);
                sz+=1;
            }
            i++;
        }
    }

public:
    CBTInserter(TreeNode *root) {
        this->root = root;
        bfs(root);
    }

    int insert(int v) {
        TreeNode *node = new TreeNode(v);
        nodes.push_back(node);
        int sz=nodes.size();
        TreeNode* parent=nodes[sz/2-1];
        cout<<"parent idx: "<<sz/2-1<<endl;
        if(sz%2==0)
            parent->left=node;
        else
            parent->right=node;
//        if(sz==1) return 0;   测试用例没有考虑构造函数调用为 CBTInserter(nullptr) 的情况
        return parent->val;
    }

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