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<?php |
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declare(strict_types=1); |
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namespace leetcode; |
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class WordBreak |
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{ |
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public static function wordBreak(string $s, array $words): bool |
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{ |
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if (strlen($s) <= 0 || count($words) <= 0) { |
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return false; |
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} |
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$dicts = array_flip(array_unique(array_values($words))); |
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$memo = array_fill(0, strlen($s), -1); |
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return self::helper($s, $dicts, 0, $memo); |
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} |
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private static function helper( |
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string $s, |
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array &$dicts, |
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int $start, |
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array &$memo |
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): bool { |
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$n = strlen($s); |
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if ($start >= $n) { |
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return true; |
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} |
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if (isset($memo[$start]) && $memo[$start] !== -1) { |
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return (bool) $memo[$start]; |
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} |
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for ($i = $start; $i <= $n; $i++) { |
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$key = substr($s, $start, $i - $start); |
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if (isset($dicts[$key]) && self::helper($s, $dicts, $i, $memo)) { |
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return (bool) ($memo[$start] = 1); |
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} |
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} |
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return (bool) ($memo[$start] = 0); |
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} |
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public static function wordBreak2(string $s, array $words) |
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{ |
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if (strlen($s) <= 0 || count($words) <= 0) { |
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return false; |
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} |
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$dicts = array_flip(array_unique(array_values($words))); |
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$dp = array_fill(0, strlen($s) + 1, false); |
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[$dp[0], $n] = [true, count($dp)]; |
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for ($i = 0; $i < $n; $i++) { |
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for ($j = 0; $j < $i; $j++) { |
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$key = substr($s, $j, $i - $j); |
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if (isset($dicts[$key]) && $dp[$j]) { |
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$dp[$i] = true; |
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break; |
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} |
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} |
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} |
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return array_pop($dp); |
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} |
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public static function wordBreak3(string $s, array $words): bool |
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{ |
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$n = strlen($s); |
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if ($n <= 0 || count($words) <= 0) { |
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return false; |
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} |
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$dicts = array_flip(array_unique(array_values($words))); |
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$visited = array_fill(0, $n, false); |
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$queue = [0]; |
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while ($queue) { |
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$start = $queue[0]; |
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array_pop($queue); |
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if (!$visited[$start]) { |
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for ($i = $start + 1; $i <= $n; $i++) { |
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$key = substr($s, $start, $i - $start); |
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if (isset($dicts[$key])) { |
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$queue[] = $i; |
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if ($i === $n) { |
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return true; |
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} |
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} |
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} |
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$visited[$start] = true; |
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} |
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} |
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return false; |
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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.