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class Solution {
public:
    enum Direciton {left,right};
    vector<vector<int>> zigzagLevelOrder(TreeNode *root) {
        vector<vector<int>> result;
        result.clear();
        vector<TreeNode*> seq,seq_c;
        seq.clear();
        if(root != NULL)seq.push_back(root);
        Direciton direction = left;
        while(seq.size() > 0) {
            seq_c.clear();
            vector<int>item;
            item.clear();
            if(direction == left) {
                direction = right;
                for(int i = 0; i < seq.size();i++) {
                    item.push_back(seq[i]->val);
                    if(seq[i]->left != NULL) {
                        seq_c.push_back(seq[i]->left);
                    }
                    if(seq[i]->right != NULL) {
                        seq_c.push_back(seq[i]->right);
                    }
                }
            }
            else {
                direction = left;
                for(int i = seq.size()-1; i >= 0; i--) {
                    item.push_back(seq[i]->val);
                }
                for(int i = 0; i < seq.size();i++) {
                    if(seq[i]->left != NULL) {
                        seq_c.push_back(seq[i]->left);
                    }
                    if(seq[i]->right != NULL) {
                        seq_c.push_back(seq[i]->right);
                    }
                }
            }
            result.push_back(item);
            seq = seq_c;
        }
        return result;
    }
};