Insufficient Nodes in Root to Leaf Paths LeetCode solution in C++

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// What we do is a basic DFS from root to leaf, here I used preorder.
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class Solution {
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 public:
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  TreeNode *sufficientSubset(TreeNode *root, int limit) {
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    // Base cases to check if there is no root node
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    if (!root) return root;
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    // or else if there are no leaf nodes to the root node and thus we simply
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    // check if the root node is less than the limit or not, if it is less we
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    // return null or else we know what to return.
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    if (!root->left && !root->right) {
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      if (root->val < limit)
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        return NULL;
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      else
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        return root;
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    } else {
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      // We then start out DFS traversal, every time decreasing the limit with
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      // the current node's value and after that, we move over ahead and check
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      // the base conditions again and see if any case has been satisfied or not
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      root->left = sufficientSubset(root->left, limit - root->val);
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      root->right = sufficientSubset(root->right, limit - root->val);
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      if (!root->left && !root->right)
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        return NULL;
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      else
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        return root;
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    }
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  }
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};