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]
]

解题思路：

class Solution {
public:
    vector<vector<int>> levelOrderBottom(TreeNode* root) {
        vector<vector<int>> res;
        vector<int> temp;
        if(root==NULL) return res;
        queue<TreeNode*> q;
        q.push(root);
        TreeNode* node;
        while(!q.empty())
        {
            queue<TreeNode*> q1;
            while(!q.empty())
            {
                node=q.front();
                q.pop();
                temp.push_back(node->val);
                if(node->left!=NULL)
                q1.push(node->left);
                if(node->right!=NULL)
                q1.push(node->right);
            }
            res.push_back(temp);
            temp.clear();
            q=q1;
        }
        reverse(res.begin(),res.end());
        return res;
    }
};