LeetCode: Binary Tree Zigzag Level Order Traversal

出错了一次，改了一次，小失误没用弄好zigzag的排序。题目还是简单的

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    void dfs(vector<vector<int>> &ret, stack<TreeNode*> &S, int num) {
        stack<TreeNode*> T;
        vector<int> level;
        while (!S.empty()) {
            TreeNode *tmp = S.top();
            level.push_back(tmp->val);
            if (num%2) {
                if (tmp->left) T.push(tmp->left);
                if (tmp->right) T.push(tmp->right);
            }
            else {
                if (tmp->right) T.push(tmp->right);
                if (tmp->left) T.push(tmp->left);
            }
            S.pop();
        }
        ret.push_back(level);
        if (!T.empty()) {
            S = T;
            dfs(ret, S, num+1);
        }
    }
    vector<vector<int> > zigzagLevelOrder(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector<vector<int>> ret;
        if (!root) return ret;
        stack<TreeNode*> S;
        S.push(root);
        dfs(ret, S, 1);
        return ret;
    }
};

 C#:

/**
 * 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>> ZigzagLevelOrder(TreeNode root) {
        Stack<TreeNode> left = new Stack<TreeNode>();
        Stack<TreeNode> right = new Stack<TreeNode>();
        List<List<int>> ans = new List<List<int>>();
        if (root == null) return ans;
        left.Push(root);
        while (left.Count != 0 || right.Count != 0)
        {
            List<int> tmp = new List<int>();
            if (left.Count != 0) {
                while (left.Count != 0) {
                    TreeNode p = left.Peek();
                    left.Pop();
                    tmp.Add(p.val);
                    if (p.left != null) right.Push(p.left);
                    if (p.right != null) right.Push(p.right);
                }
            }
            else {
                while (right.Count != 0) {
                    TreeNode p = right.Peek();
                    right.Pop();
                    tmp.Add(p.val);
                    if (p.right != null) left.Push(p.right);
                    if (p.left != null) left.Push(p.left);
                }
            }
            ans.Add(tmp);
        }
        return ans;
    }
}