Maximum Difference Between Node and Ancestor LeetCode solution in C++

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class Solution {
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 private:
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  int maxDiff;
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  pair<int, int> helper(TreeNode *root) {
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    if (root == NULL) return {INT_MAX, INT_MIN};
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    pair<int, int> L = helper(root->left), R = helper(root->right);
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    pair<int, int> minMax = {min(L.first, R.first), max(L.second, R.second)};
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    if (minMax.first != INT_MAX)
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      maxDiff = max(maxDiff, max(abs(root->val - minMax.first), abs(root->val - minMax.second)));
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    return {min(root->val, minMax.first), max(root->val, minMax.second)};
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  }
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 public:
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  int maxAncestorDiff(TreeNode *root) {
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    maxDiff = INT_MIN;
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    helper(root);
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    return maxDiff;
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  }
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};