[LeetCode] Binary Tree Level Order Traversal II

iven 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]
]

思路：思路和Binary Tree Level Order Traversal相同，在最后的时候reverse.

/**
* 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> > result;
if (root == NULL) return result;

vector<int> level;

queue<TreeNode* > q;
q.push(root);
q.push(0);

while(!q.empty()) {
TreeNode* p = q.front();
q.pop();
if (p != NULL) {
level.push_back(p->val);
if (p->left) q.push(p->left);
if (p->right) q.push(p->right);
} else {
result.push_back(level);
level.clear();

if (!q.empty())
q.push(0);
}
}

reverse(result.begin(), result.end());

return result;
}
};