leetcode[107]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]

]

 

confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.

/**

 * Definition for binary tree

 * 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>> res;

        vector<int> tmp;

        queue<TreeNode *> Qpre,Qcurr;

        if(root==NULL)return res;

        else

        {

            Qpre.push(root);

            while(1)

            {

                while(!Qpre.empty())

                {

                  TreeNode *tem=Qpre.front();

                  Qpre.pop();

                  tmp.push_back(tem->val);

                  if(tem->left)Qcurr.push(tem->left);

                  if(tem->right)Qcurr.push(tem->right);

                }

                res.push_back(tmp);

                tmp.clear();

                if(Qcurr.empty())break;

                else Qcurr.swap(Qpre);

            }

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

            return res;

        }        

    }

};