lintcode-二叉树的层次遍历 II

描述

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）

样例

给出一棵二叉树 {3,9,20,#,#,15,7},

    3   / \  9  20    /  \   15   7

按照从下往上的层次遍历为：

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

代码

/** * Definition of TreeNode: * class TreeNode { * public: *     int val; *     TreeNode *left, *right; *     TreeNode(int val) { *         this->val = val; *         this->left = this->right = NULL; *     } * } */#include<queue>#include<algorithm>class Solution {public:    /*     * @param root: A tree     * @return: buttom-up level order a list of lists of integer     */    vector<vector<int>> levelOrderBottom(TreeNode * root) {        // write your code here        TreeNode * q=root;        vector<vector<int>> res;        if(root==NULL){            return res;        }        queue<TreeNode *> childs;        childs.push(q);        TreeNode * tt=NULL;        int len=1;        while(!childs.empty()){            vector<int> temp;            len=childs.size();            while(len--){                temp.push_back(childs.front()->val);                tt=childs.front();                childs.pop();                if(tt->left!=NULL){                    childs.push(tt->left);                }                if(tt->right!=NULL){                    childs.push(tt->right);                }               }            res.push_back(temp);        }         reverse(res.begin(),res.end());        return res;    }};