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47 lines
1.8 KiB
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47 lines
1.8 KiB
HTML
<p>Given a <strong>binary tree</strong> <code>root</code>, return <em>the maximum sum of all keys of <strong>any</strong> sub-tree which is also a Binary Search Tree (BST)</em>.</p>
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<p>Assume a BST is defined as follows:</p>
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<ul>
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<li>The left subtree of a node contains only nodes with keys <strong>less than</strong> the node's key.</li>
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<li>The right subtree of a node contains only nodes with keys <strong>greater than</strong> the node's key.</li>
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<li>Both the left and right subtrees must also be binary search trees.</li>
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</ul>
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<p> </p>
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<p><strong class="example">Example 1:</strong></p>
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<p><img alt="" src="https://assets.leetcode.com/uploads/2020/01/30/sample_1_1709.png" style="width: 320px; height: 250px;" /></p>
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<pre>
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<strong>Input:</strong> root = [1,4,3,2,4,2,5,null,null,null,null,null,null,4,6]
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<strong>Output:</strong> 20
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<strong>Explanation:</strong> Maximum sum in a valid Binary search tree is obtained in root node with key equal to 3.
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</pre>
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<p><strong class="example">Example 2:</strong></p>
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<p><img alt="" src="https://assets.leetcode.com/uploads/2020/01/30/sample_2_1709.png" style="width: 134px; height: 180px;" /></p>
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<pre>
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<strong>Input:</strong> root = [4,3,null,1,2]
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<strong>Output:</strong> 2
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<strong>Explanation:</strong> Maximum sum in a valid Binary search tree is obtained in a single root node with key equal to 2.
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</pre>
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<p><strong class="example">Example 3:</strong></p>
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<pre>
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<strong>Input:</strong> root = [-4,-2,-5]
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<strong>Output:</strong> 0
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<strong>Explanation:</strong> All values are negatives. Return an empty BST.
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</pre>
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<p> </p>
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<p><strong>Constraints:</strong></p>
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<ul>
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<li>The number of nodes in the tree is in the range <code>[1, 4 * 10<sup>4</sup>]</code>.</li>
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<li><code>-4 * 10<sup>4</sup> <= Node.val <= 4 * 10<sup>4</sup></code></li>
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</ul>
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