LeetCode: Binary Tree Level Order Traversal

C++

 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>> levelOrder(TreeNode* root) {

13         vector<vector<int>> ans;

14         if (root == NULL) return ans;

15         vector<int> tmp;

16         queue<TreeNode *> que;

17         que.push(root);

18         que.push(NULL);

19         while (true) {

20             TreeNode *front = que.front();

21             que.pop();

22             if (front == NULL) {

23                 ans.push_back(tmp);

24                 if (que.empty() || que.front() == NULL) break;

25                 tmp.clear();

26                 que.push(NULL);

27             }

28             else {

29                 if (front->left) que.push(front->left);

30                 if (front->right) que.push(front->right);

31                 tmp.push_back(front->val);

32             }

33         }

34         return ans;

35     }

36 };

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C#代码：

 1 /**

 2  * Definition for a binary tree node.

 3  * public class TreeNode {

 4  *     public int val;

 5  *     public TreeNode left;

 6  *     public TreeNode right;

 7  *     public TreeNode(int x) { val = x; }

 8  * }

 9  */

10 public class Solution {

11     public List<List<int>> LevelOrder(TreeNode root) {

12         List<List<int>> ans = new List<List<int>>();

13         if (root == null) return ans;

14         List<int> tmp = new List<int>();

15         Queue<TreeNode> que = new Queue<TreeNode>();

16         que.Enqueue(root);

17         que.Enqueue(null);

18         while (true)

19         {

20             TreeNode peek = que.Peek();

21             que.Dequeue();

22             if (peek == null)

23             {

24                 ans.Add(tmp);

25                 if (que.Count == 0 || que.Peek() == null) break;

26                 tmp = new List<int>();

27                 que.Enqueue(null);

28             }

29             else {

30                 if (peek.left != null) que.Enqueue(peek.left);

31                 if (peek.right != null) que.Enqueue(peek.right);

32                 tmp.Add(peek.val);

33             }

34         }

35         return ans;

36     }

37 }

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