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
#include
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 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;
    }
};