337

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int rob(TreeNode* root) {
        auto p = dfs(root);
        return max(p.first, p.second);
    }

    pair<int, int> dfs(TreeNode* root){
        // First -> including current node;
        // Second -> excluding current node / Get max of previous elements sum;
        pair<int, int> sum  = {0, 0};
        if(!root) return sum;

        // Dfs on left and right subtree.
        auto left = dfs(root->left);
        auto right = dfs(root->right);

        // If current element is included.
        sum.first = root->val + left.second + right.second;

        // If current element is excluded, get max of last element.
        sum.second = max(left.first, left.second) + max(right.first, right.second);
        return sum;
    }
};