Binary Tree Zigzag Level Order Traversal LeetCode solution in C++

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class Solution {
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 public:
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  vector<vector<int>> zigzagLevelOrder(TreeNode *root) {
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    vector<vector<int>> ans;
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    if (!root) return ans;
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    vector<int> r;
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    queue<TreeNode *> q;
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    int count = 1;
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    q.push(root);
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    q.push(NULL);
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    while (1) {
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      if (q.front() == NULL) {
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        q.pop();
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        if (count % 2 == 0) reverse(r.begin(), r.end());
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        ans.push_back(r);
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        if (q.empty()) return ans;
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        q.push(NULL);
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        r.resize(0);
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        count++;
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        continue;
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      }
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      r.push_back((q.front())->val);
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      if (q.front()->left) q.push((q.front())->left);
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      if (q.front()->right) q.push((q.front())->right);
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      q.pop();
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    }
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    return ans;
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  }
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};