Leetcode60: 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,#,#,15,7}

,

3
/ \
9  20
/  \
15   7

return its bottom-up level order traversal as:

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

/**
* 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) {
queue<TreeNode*> q1;
vector<vector<int>> result;
vector<int> temp;
if(!root)
return result;
q1.push(root);
do
{
queue<TreeNode*> q2;
temp.clear();
while(!q1.empty())
{
TreeNode* Node = q1.front();
q1.pop();
temp.push_back(Node->val);
if(Node->left)
q2.push(Node->left);
if(Node->right)
q2.push(Node->right);
}
q1 = q2;
result.push_back(temp);
}while(!q1.empty());
reverse(result.begin(),result.end());
return result;
}
};