[LeetCode] Binary Tree Level Order Traversal II

[Problem]
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],
]

[Solution]

class Solution {
public:
vector<vector<int> > levelOrderBottom(TreeNode *root) {
// Start typing your C/C++ solution below
// DO NOT write int main() function

// result
vector<vector<int> > res;
if(NULL == root)return res;

// store tmp result in stack
stack<vector<int> > mStack;
queue<vector<TreeNode*> > mQueue;

// add root node
vector<TreeNode*> tmp;
tmp.push_back(root);
mQueue.push(tmp);

// level order
while(!mQueue.empty()){
vector<int> levelRes;
vector<TreeNode*> levelNode;

// iterate
vector<TreeNode*> nodes = mQueue.front();
vector<TreeNode*>::iterator it;
for(it = nodes.begin(); it != nodes.end(); ++it){
levelRes.push_back((*it)->val);
if((*it)->left != NULL){
levelNode.push_back((*it)->left);
}
if((*it)->right != NULL){
levelNode.push_back((*it)->right);
}
}
mStack.push(levelRes);
mQueue.pop();
if(levelNode.size() > 0){
mQueue.push(levelNode);
}
}

// result
while(!mStack.empty()){
res.push_back(mStack.top());
mStack.pop();
}
return res;
}
};

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