[LeetCode] Binary Tree Level Order Traversal II

iven 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]
]

思路：思路和Binary Tree Level Order Traversal相同，在最后的时候reverse.

 1 /**
 2  * Definition for a binary tree node.
 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>> levelOrderBottom(TreeNode* root) {
13         vector<vector<int> > result;
14         if (root == NULL) return result;
15         
16         vector<int> level;
17         
18         queue<TreeNode* > q;
19         q.push(root);
20         q.push(0);
21         
22         while(!q.empty()) {
23             TreeNode* p = q.front();
24             q.pop();
25             if (p != NULL) {
26                 level.push_back(p->val);
27                 if (p->left) q.push(p->left);
28                 if (p->right) q.push(p->right);
29             } else {
30                 result.push_back(level);
31                 level.clear();
32                 
33                 if (!q.empty())
34                     q.push(0);
35             }
36         }
37         
38         reverse(result.begin(), result.end());
39         
40         return result;
41     }
42 };

 

posted @ 2015-01-16 21:09  vincently  阅读(225)  评论(0)  编辑  收藏  举报