leetcod Binary Tree Level Order Traversal II

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.

對於反轉的操作也是Leetcode慣出的題目，或者說面試慣考的題目，知道怎麼應付就好辦，順序遍歷，然後reverse就可以了。

class Solution {
public:
	vector > levelOrderBottom(TreeNode *root) 
	{
		vector > v;
		if (!root) return v;

		queue qt1;
		qt1.push(root);
		queue qt2;

		vector itmedia;
		
		while (!qt1.empty())
		{
			while (!qt1.empty())
			{
				TreeNode *t = qt1.front();
				qt1.pop();
				itmedia.push_back(t->val);
				if (t->left) qt2.push(t->left);
				if (t->right) qt2.push(t->right);
			}
			v.push_back(itmedia);
			itmedia.clear();
			qt2.swap(qt1);
		}
		reverse(v.begin(), v.end());
		return v;
	}
};