力扣-107题二叉树的层序遍历 II（C++）- 层序遍历中的出错点

快来打我* 2022-09-01 14:59 179阅读 0赞

题目链接：[https://leetcode-cn.com/problems/binary-tree-level-order-traversal-ii/][https_leetcode-cn.com_problems_binary-tree-level-order-traversal-ii]  
题目如下：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNDY3Njcw_size_16_color_FFFFFF_t_70]

/**
     * 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;
            
        }
    };

[https_leetcode-cn.com_problems_binary-tree-level-order-traversal-ii]: https://leetcode-cn.com/problems/binary-tree-level-order-traversal-ii/
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNDY3Njcw_size_16_color_FFFFFF_t_70]: /images/20220829/915f4013a9d8443da5b3f03f1f07ecbd.png