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<?php |
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declare(strict_types=1); |
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namespace leetcode; |
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use leetcode\util\TreeNode; |
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class BinaryTreeMaximumPathSum |
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{ |
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public static function maxPathSum(TreeNode $root): int |
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{ |
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$max = PHP_INT_MIN; |
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self::helper($root, $max); |
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return $max; |
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} |
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public static function maxPathSum2(TreeNode $root): int |
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{ |
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$helper = static function (TreeNode $node) { |
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[$order, $stack] = [[], [$node]]; |
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while ($stack) { |
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$top = array_pop($stack); |
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array_push($order, $top); |
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if ($top->left) { |
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array_push($stack, $top->left); |
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} |
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if ($top->right) { |
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array_push($stack, $top->right); |
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} |
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} |
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return array_reverse($order); |
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}; |
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if (!$root->left && !$root->right) { |
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return $root->val; |
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} |
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[$ans, $map] = [PHP_INT_MIN, []]; |
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$nodes = $helper($root); |
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foreach ($nodes as $node) { |
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$left = $right = 0; |
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if ($node->left) { |
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$left = spl_object_hash($node->left); |
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} |
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if ($node->right) { |
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$right = spl_object_hash($node->right); |
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} |
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$left = max(0, $map[$left] ?? 0); |
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$right = max(0, $map[$right] ?? 0); |
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$map[spl_object_hash($node)] = max($left, $right) + $node->val; |
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$ans = max($ans, $left + $node->val + $right); |
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} |
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return $ans; |
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} |
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private static function helper(?TreeNode $node, int &$max): int |
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{ |
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if (! $node) { |
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return 0; |
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} |
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$left = max(0, self::helper($node->left, $max)); |
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$right = max(0, self::helper($node->right, $max)); |
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$max = max($max, $left + $right + $node->val); |
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return max($left, $right) + $node->val; |
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} |
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} |
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imajinyun /
leetcode-php
This check marks implicit conversions of arrays to boolean values in a comparison. While in PHP an empty array is considered to be equal (but not identical) to false, this is not always apparent.
Consider making the comparison explicit by using
empty(..)or! empty(...)instead.