[数据结构与算法]力扣-107题 二叉树的层序遍历 II（C++）- 层序遍历中的出错点

题目链接：https://leetcode-cn.com/problems/binary-tree-level-order-traversal-ii/
题目如下：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    vector<vector<int>> levelOrderBottom(TreeNode* root) {
        vector<vector<int>> result;
        if(root==NULL) return result;

        queue<TreeNode*> que;
        que.push(root);

        while(!que.empty()){
            int size=que.size();
            vector<int> temp;

            while(size--){//que.size()!=0不能换成这个
                TreeNode* node=que.front();
                que.pop();

                temp.push_back(node->val);

                if(node->left!=NULL) que.push(node->left);
                if(node->right!=NULL) que.push(node->right);
            }
            result.push_back(temp);
        }
		
		//注意写法及用法
        reverse(result.begin(),result.end());

        return result;
        
    }
};