[LeetCode] Binary Tree Level Order Traversal II

[Problem]

Given a binary tree, return the bottom-up level ordertraversal of its nodes' values. (ie, from left to right, level bylevel 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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