leetcode: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]
]
这个题目很有意思。是要你从尾部到顶部，从左到右，然后输出一个内容是一个<int>容器的容器。
 1 /**
 2  * Definition for binary tree
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     vector<vector<int> > out;//新建要返回的容器
13     void levelTraval(vector<TreeNode* >& level)
14     {
15         if(level.size() > 0)
16         {
17             vector<TreeNode*> nextLevel;
18             for(int i = 0; i < level.size(); i++)
19             {
20                 if(level[i]->left)
21                     nextLevel.push_back(level[i]->left);
22                 if(level[i]->right)
23                     nextLevel.push_back(level[i]->right);
24             }
25             levelTraval(nextLevel);
26             vector<int> val;
27             for(int i = 0; i < level.size(); i++)
28                 val.push_back(level[i]->val);
29             out.push_back(val);
30         }
31     }
32     vector<vector<int> > levelOrderBottom(TreeNode *root) {
33         // Start typing your C/C++ solution below
34         // DO NOT write int main() function
35         out.clear();
36         vector<TreeNode*> v;
37         if(root != NULL)
38         {
39             v.push_back(root);
40             levelTraval(v);
41         }
42         return out;
43     }
44  };

 

posted on 2015-04-26 22:18  何氏小萌  阅读(119)  评论(0)    收藏  举报