[leetcode] Binary Tree Level Order Traversal II

From : https://leetcode.com/problems/binary-tree-level-order-traversal-ii/

Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from left to right, level by level from leaf to root).

For example:
Given binary tree {3,9,20,#,#,15,7},

    3   / \  9  20    /  \   15   7

return its bottom-up level order traversal as:

[  [15,7],  [9,20],  [3]]

confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.

/** * Definition for a binary tree node. * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    vector<vector<int>> levelOrderBottom(TreeNode* root) {        vector<vector<int>> res;        if(root) {            queue<TreeNode> box;            box.push(*root);            int num=1, newNum=0;            while(num) {                vector<int> cur;                while(num) {                    TreeNode node = box.front();                    box.pop();                    num--;                    cur.push_back(node.val);                    if(node.left)  {box.push(*node.left); newNum++;}                    if(node.right) {box.push(*node.right);newNum++;}                                    }                res.insert(res.begin(), cur);                num = newNum;                newNum = 0;            }        }        return res;    }};