<p>The thief has found himself a new place for his thievery again. There is only one entrance to this area, called <code>root</code>.</p> <p>Besides the <code>root</code>, each house has one and only one parent house. After a tour, the smart thief realized that all houses in this place form a binary tree. It will automatically contact the police if <strong>two directly-linked houses were broken into on the same night</strong>.</p> <p>Given the <code>root</code> of the binary tree, return <em>the maximum amount of money the thief can rob <strong>without alerting the police</strong></em>.</p> <p> </p> <p><strong class="example">Example 1:</strong></p> <img alt="" src="https://assets.leetcode.com/uploads/2021/03/10/rob1-tree.jpg" style="width: 277px; height: 293px;" /> <pre> <strong>Input:</strong> root = [3,2,3,null,3,null,1] <strong>Output:</strong> 7 <strong>Explanation:</strong> Maximum amount of money the thief can rob = 3 + 3 + 1 = 7. </pre> <p><strong class="example">Example 2:</strong></p> <img alt="" src="https://assets.leetcode.com/uploads/2021/03/10/rob2-tree.jpg" style="width: 357px; height: 293px;" /> <pre> <strong>Input:</strong> root = [3,4,5,1,3,null,1] <strong>Output:</strong> 9 <strong>Explanation:</strong> Maximum amount of money the thief can rob = 4 + 5 = 9. </pre> <p> </p> <p><strong>Constraints:</strong></p> <ul> <li>The number of nodes in the tree is in the range <code>[1, 10<sup>4</sup>]</code>.</li> <li><code>0 <= Node.val <= 10<sup>4</sup></code></li> </ul>