Binary Tree Maximum Path Sum LeetCode solution in C++

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class Solution {
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 public:
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  int rec(TreeNode *root, int &res) {
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    if (root == nullptr) return 0;
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    // maximum value from left
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    int l = rec(root->left, res);
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    // maximum value from right
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    int r = rec(root->right, res);
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    // check if path can go through this node ,if yes upadte the result value
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    res = max(res, root->val + l + r);
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    // return the maximum non-negative path value
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    return max({l + root->val, r + root->val, 0});
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  }
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  int maxPathSum(TreeNode *root) {
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    int res = INT_MIN;
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    int x = rec(root, res);
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    return res;
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  }
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};