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],
]

就是Binary Tree Level Order Traversal的基础上reverse

vector<vector<int> > levelOrderBottom(TreeNode *root)
{
vector<vector<int> > ret;
if(root == NULL)
return ret;

vector<int> vec;
queue<TreeNode *> Q;

Q.push(root);
int count = 1;

while(!Q.empty())
{
vec.clear();
int nextCount = 0;
for(int i = 0; i < count; i++)
{
TreeNode *tmp = Q.front();
Q.pop();

vec.push_back(tmp->val);
if(tmp->left)
{
Q.push(tmp->left);
nextCount++;
}
if(tmp->right)
{
Q.push(tmp->right);
nextCount++;
}
}
count = nextCount;
ret.push_back(vec);
}
reverse(ret.begin(),ret.end());
return ret;
}