LeetCode: Binary Tree Level Order Traversal

C++

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<vector<int>> levelOrder(TreeNode* root) {
        vector<vector<int>> ans;
        if (root == NULL) return ans;
        vector<int> tmp;
        queue<TreeNode *> que;
        que.push(root);
        que.push(NULL);
        while (true) {
            TreeNode *front = que.front();
            que.pop();
            if (front == NULL) {
                ans.push_back(tmp);
                if (que.empty() || que.front() == NULL) break;
                tmp.clear();
                que.push(NULL);
            }
            else {
                if (front->left) que.push(front->left);
                if (front->right) que.push(front->right);
                tmp.push_back(front->val);
            }
        }
        return ans;
    }
};

C#代码：

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public List<List<int>> LevelOrder(TreeNode root) {
        List<List<int>> ans = new List<List<int>>();
        if (root == null) return ans;
        List<int> tmp = new List<int>();
        Queue<TreeNode> que = new Queue<TreeNode>();
        que.Enqueue(root);
        que.Enqueue(null);
        while (true)
        {
            TreeNode peek = que.Peek();
            que.Dequeue();
            if (peek == null)
            {
                ans.Add(tmp);
                if (que.Count == 0 || que.Peek() == null) break;
                tmp = new List<int>();
                que.Enqueue(null);
            }
            else {
                if (peek.left != null) que.Enqueue(peek.left);
                if (peek.right != null) que.Enqueue(peek.right);
                tmp.Add(peek.val);
            }
        }
        return ans;
    }
}