LeetCode-103.Binary Tree Zigzag Level Order Traversal

Given a binary tree, return the zigzag level order traversal of its nodes' values. (ie, from left to right, then right to left for the next level and alternate between).

For example:

Given binary tree 

{3,9,20,#,#,15,7}

,

3
/ \
9  20
/  \
15   7

return its zigzag level order traversal as:

[
[3],
[20,9],
[15,7]
]

这道题其实都与LeetCode 104的解法(http://blog.csdn.net/zmq570235977/article/details/51210982)基本一样

也是102和107的变种(http://blog.csdn.net/zmq570235977/article/details/51325927)

public IList<IList<int>> ZigzagLevelOrder(TreeNode root)
{
IList<IList<int>> res = new List<IList<int>>();
if (root == null)
return res;
int num;
bool isLeft = true;
TreeNode node;
Queue<TreeNode> q = new Queue<TreeNode>();
q.Enqueue(root);
while ((num = q.Count) > 0)
{
IList<int> list = new List<int>();
for (int i = 0; i < num; i++)
{
node = q.Dequeue();
if (node.left != null)
q.Enqueue(node.left);
if (node.right != null)
q.Enqueue(node.right);
if (isLeft)
list.Add(node.val);
else
list.Insert(0,node.val);
}
res.Add(list);
isLeft = !isLeft;
}
return res;
}