/**
 * 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) {
        queue<TreeNode*> q;
        q.push(root);
        vector<vector<int>> v;
        if(root==NULL) return v;
        bool p=true;
        while(!q.empty())
        {
            vector<int> v2;
            int p2=q.size();
            while(p2--)
            {
                TreeNode* temp=q.front();
                q.pop();
                v2.push_back(temp->val);
                if(temp->left) q.push(temp->left);
                if(temp->right) q.push(temp->right);
            }
            
            if(!p) 
            {
                reverse(v2.begin(), v2.end());
                p=true;
            }
            else p=false;
            v.push_back(v2);
        }
        return v;
    }
};