/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    vector<vector<int>> zigzagLevelOrder(TreeNode* root) {
        vector<TreeNode*> ret;
        vector<vector<int>> re;
        if (!root) return re;
        ret.push_back(root);
        int i = 0;
        while (!ret.empty()) {
            vector<TreeNode*> t;
            vector<int> temp;
            for (int i = 0; i < ret.size(); i++) {
                temp.push_back(ret[i]->val);
                if (ret[i]->left != nullptr)
                    t.push_back(ret[i]->left);
                if (ret[i]->right != nullptr)
                    t.push_back(ret[i]->right);
            }
            if (i % 2 == 0)
                re.push_back(temp);
            else {
                int len = temp.size();
                for (int i = 0; i < len / 2; i++) {
                    swap(temp[i], temp[len - i - 1]);
                }
                re.push_back(temp);
            }
            i++;
            ret = t;
        }
        return re;
    }
};