Maximum sum of Non-adjacent nodes

Given a binary tree with a value associated with each node, we need to choose a subset of these nodes such that sum of chosen nodes is maximum under a constraint that no two chosen node in subset should be directly connected that is, if we have taken a node in our sum then we can’t take its any children or parents in consideration and vice versa.

• Time : O(n)
• Space : O(1)

class Solution{
    pair<int, int> helper(Node* node) {
        if(!node) return {0, 0};
        auto l = helper(node->left);
        auto r = helper(node->right);

        auto adj = l.second + r.second + node->data;
        auto nonadj = r.first + l.first;
        return {adj, max({r.first + l.first, r.first + l.second, r.second + l.first, r.second + l.second})};
    }
public:
    //Function to return the maximum sum of non-adjacent nodes.
    int getMaxSum(Node *root)
    {
        auto res = helper(root);
        return max(res.first, res.second);
    }
};