leetcode107 二叉树的层次遍历2

/*
 * @lc app=leetcode.cn id=107 lang=cpp
 *
 * [107] 二叉树的层次遍历 II
 */

// @lc code=start
/**
 * 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:
//和102一样的思路，最后加一个翻转
    vector<vector<int>> levelOrderBottom(TreeNode* root) {
        if(!root) return {};
        vector<vector<int>> res;
        queue<TreeNode*> q;

        q.push(root);
        while(!q.empty()){
            int len=q.size();
            vector<int> tmp;
            for(int i=0;i<len;i++){
                TreeNode* node=q.front();
                q.pop();
                tmp.push_back(node->val);
                if(node->left) q.push(node->left);
                if(node->right) q.push(node->right);
            }
            res.push_back(tmp);

        }
        reverse(res.begin(),res.end());
        return res;
    }
};
// @lc code=end