LeetCode | 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 

思路：與Binary Tree Level Order Traversal這題一致，就是將最後的結果倒置一下即可。

class Solution {
public:
    vector<vector<int> > levelOrderBottom(TreeNode *root) 
	{
		queue<TreeNode*> L;
		TreeNode* temp;
		vector<int>v;
		vector<TreeNode*>vt;
		vector<vector<int> >vv;
		if(root)
		{
			v.push_back(root->val);
			vv.push_back(v);
		}
		L.push(root);
		while(!L.empty())
		{
			temp = L.front();
			vt.push_back(temp);
			L.pop();
			if(!temp)
				continue;
			L.push(temp->left);	
			L.push(temp->right);	
		}
		int i,j,cnt=0;
		int step = 3;
		for(i=1; i<vt.size(); i=j)
		{
			v.clear();
			for(j=i; j<step && j<vt.size(); j++)
			{
				if(vt[j]!=NULL)
				{
					v.push_back(vt[j]->val);
					cnt+=2;
				}
			}
			step = j+cnt;
			cnt = 0;
			if(j<vt.size())
				vv.push_back(v);
		}
		reverse(vv.begin(), vv.end());//結果倒置
        return vv;
    }
};