Leetcode 107 Binary Tree Level Order Traversal II 二叉树+BFS

题意是倒过来层次遍历二叉树

下面我介绍下BFS的基本框架，所有的BFS都是这样写的

struct Nodetype {
      int d;//层数即遍历深度
      KeyType m;//相应的节点值
}
queue<Nodetype> q;
q.push(firstnode);
while(!q.empty()){
        Nodetype now = q.front();
         q.pop();
         ........
         for(遍历所有now点的相邻点next){
               if(!visit[next]) {
                   访问每个没有访问过的点;
                   做相应的操作；
                   next.d = now.d + 1;
                   q.push(next);
               }
         }         
  }

 

对于二叉树将val看成层数，这边我偷懒了。

 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         
14         vector<vector<int>> v;
15         if(!root) return v;
16         vector<int> t;
17         
18         t.push_back(root->val);
19         v.push_back(t);
20         root->val = 1;
21         
22         queue<TreeNode*> q;
23         q.push(root);
24         
25         while(!q.empty()){
26             TreeNode* now = q.front();
27             q.pop();
28             if(!now) continue;
29             
30             q.push(now->left);
31             q.push(now->right);
32             if(now->val < v.size()){
33                 if(now->left) v[now->val].push_back(now->left->val);
34                 if(now->right) v[now->val].push_back(now->right->val);
35             }
36             else{
37                 vector<int> t;        
38                 if(now->left) t.push_back(now->left->val);
39                 if(now->right) t.push_back(now->right->val);
40                 if(t.size() != 0)v.push_back(t);
41             }
42             if(now->left) now->left->val = now->val + 1;
43             if(now->right)now->right->val = now->val + 1;
44         }
45         reverse(v.begin(),v.end());
46         return v;
47     }
48 };

 

posted @ 2016-03-01 20:23  Breeze0806  阅读(209)  评论(0)  编辑  收藏  举报