中等 二叉树的层次遍历 II 查看执行结果 

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通过

给出一棵二叉树，返回其节点值从底向上的层次序遍历（按从叶节点所在层到根节点所在的层遍历，然后逐层从左往右遍历）

您在真实的面试中是否遇到过这个题？ 

Yes

例子

给出一棵二叉树 {3,9,20,#,#,15,7},

3   / \  9  20    /  \   15   7

依照从下往上的层次遍历为：

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

]

asd

/** * Definition of TreeNode: * class TreeNode { * public: *     int val; *     TreeNode *left, *right; *     TreeNode(int val) { *         this->val = val; *         this->left = this->right = NULL; *     } * } */  class Solution {    /**     * @param root : The root of binary tree.     * @return : buttom-up level order a list of lists of integer     */public:    vector
     
      
       > levelOrderBottom(TreeNode *root) {         vector
       
        
         > res;        if(root == nullptr) {            return res;        }        vector
         
           temp;        queue
          
            q; stack
           
            
             > s; q.push(root); int i = 1;// points every level int j = 0;// lost point every level while(!q.empty()) { TreeNode *p = q.front(); q.pop(); if (p==nullptr) { ++j; } else { temp.push_back(p->val); q.push(p->left); q.push(p->right); } if (i == (temp.size() + j) && temp.size()!=0) { s.push(temp); temp.clear(); i*=2; j*=2; } } while(!s.empty()) { res.push_back(s.top()); s.pop(); } return res; }};