给定一个二叉树，返回其节点值自底向上的层次遍历。 （即按从叶子节点所在层到根节点所在的层，逐层从左向右遍历）

例如：
给定二叉树 [3,9,20,null,null,15,7],

    3/ \9  20/  \15   7

返回其自底向上的层次遍历为：

[[15,7],[9,20],[3]
]

解法一： 

/*** Definition for a binary tree node.* 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) {if(!root) return {};queue<TreeNode *> qu;qu.push(root);vector<vector<int>> res;while(!qu.empty()){vector<int> temp;int n = qu.size();while(n--){TreeNode * s = qu.front();qu.pop();temp.push_back(s->val);if(s->left) qu.push(s->left);if (s->right) qu.push(s->right);}res.insert(res.begin(), temp);}return res;      }
};

解法二：

/*** Definition for a binary tree node.* 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>> result;vector<int> temp;queue<TreeNode*> TreeQueue;stack<vector<int>> TreeStack;unsigned long cursize = 0;if (root == NULL){return result;}TreeQueue.push(root);while (TreeQueue.size() != 0){cursize = TreeQueue.size();for (unsigned int index = 0; index < cursize; index++){TreeNode* indexnode = TreeQueue.front();TreeQueue.pop();temp.push_back(indexnode->val);if (indexnode->left != NULL){TreeQueue.push(indexnode->left);}if (indexnode->right != NULL){TreeQueue.push(indexnode->right);}}TreeStack.push(temp);temp.clear();}while (TreeStack.empty() != true){result.push_back(TreeStack.top());TreeStack.pop();}return result;}
};