题目描述：
FDFD5B22-BB20-42E2-91A9-016D01E294FC.png
代码：递归，先按顺序遍历，再反转
/**
* 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;
vector<vector<int>> res2;
pre(root, 0, res);
for(int i=res.size()-1; i>=0; i--)
{
res2.push_back(res[i]);
}
return res2;
}
void pre(TreeNode* root, int depth, vector<vector<int>> &res)
{
if(!root)
return;
if(depth>=res.size())
res.push_back(vector<int>());
res[depth].push_back(root->val);
pre(root->left, depth+1, res);
pre(root->right, depth+1, res);
}
};
