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,null,null,15,7]

,

3
/ \
9  20
/  \
15   7

return its bottom-up level order traversal as:

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

Subscribe to see which companies asked this question
把上个的结果逆序就可以；
/**
* 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 == NULL) return res;
queue<TreeNode*>q;
q.push(root);
while(!q.empty()){
vector<int>p;
int _size = q.size();
for(int i = 0; i < _size; i++){
TreeNode *temp = q.front();
q.pop();
p.push_back(temp->val);
if(temp->left)
q.push(temp->left);
if(temp->right)
q.push(temp->right);
}
res.push_back(p);
}
reverse(res.begin(), res.end());

return res;
}
};