Find Largest Value in Each Tree Row LeetCode solution in C++

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class Solution {
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 public:
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  vector<int> res;
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  vector<int> largestValues(TreeNode *root) {
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    if (!root) return {};
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    if (!root->left && !root->right) return {root->val};
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    TreeNode *temp;
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    int mx = INT_MIN;
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    queue<TreeNode *> q;
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    q.push(root);
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    while (!q.empty()) {
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      int sz = q.size();
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      while (sz--) {
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        temp = q.front();
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        if (temp->val > mx) mx = temp->val;
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        q.pop();
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        if (temp->left) q.push(temp->left);
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        if (temp->right) q.push(temp->right);
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      }
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      res.push_back(mx);
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      mx = INT_MIN;
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    }
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    return res;
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  }
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};