houseRobberiii.java

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public int rob(TreeNode root) {
        int[] res = dfs(root);
        return Math.max(res[0],res[1]);
    }

    private int[] dfs(TreeNode root){
        if(root == null) return new int[2];

        int[] left = dfs(root.left);
        int[] right = dfs(root.right);
    
        int rob = root.val + left[1] + right[1];
        int not = Math.max(left[0],left[1]) + Math.max(right[0],right[1]);

        return new int[]{rob,not};
    }
}