int robUtil(TreeNode* root, int& nxt) {

if(!root) { nxt = 0; return 0; }

int nxt1 = 0, nxt2 = 0;

int leftSum = robUtil(root->left, nxt1);

int rightSum = robUtil(root->right, nxt2);

nxt = max(leftSum, nxt1) + max(rightSum, nxt2);

return nxt1 + root->val + nxt2;

}

int rob(TreeNode* root) {

int result2;

int result = robUtil(root, result2);

return max(result, result2);

}

pair<int, int> robUtil(TreeNode* root) {

if(!root) { return {0, 0}; }

auto leftSum = robUtil(root->left);

auto rightSum = robUtil(root->right);

return {leftSum.second + root->val + rightSum.second, max(leftSum.first, leftSum.second) + max(rightSum.first, rightSum.second)};

}

int rob(TreeNode* root) {

pair<int, int> result = robUtil(root);

return max(result.first, result.second);

}