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<?php |
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declare(strict_types=1); |
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5
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namespace leetcode; |
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7
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class EvaluateReversePolishNotation |
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{ |
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public static function evalRPN(array $tokens): int |
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{ |
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if (empty($tokens)) { |
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return 0; |
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} |
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$stack = new \SplStack(); |
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foreach ($tokens as $token) { |
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if ($token === "+") { |
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$stack->push($stack->pop() + $stack->pop()); |
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} elseif ($token === "-") { |
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[$b, $a] = [$stack->pop(), $stack->pop()]; |
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$stack->push($a - $b); |
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} elseif ($token === '*') { |
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$stack->push($stack->pop() * $stack->pop()); |
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} elseif ($token === '/') { |
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[$b, $a] = [$stack->pop(), $stack->pop()]; |
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$stack->push((int)($a / $b)); |
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} else { |
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$stack->push((int)$token); |
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} |
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} |
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return $stack->pop(); |
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} |
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public static function evalRPN2(array $tokens): int |
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{ |
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if (empty($tokens)) { |
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return 0; |
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} |
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$stack = []; |
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foreach ($tokens as $token) { |
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if (!in_array($token, ['+', '-', '*', '/'])) { |
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array_push($stack, (int)$token); |
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} else { |
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[$r, $l] = [array_pop($stack), array_pop($stack)]; |
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if ($token === '+') { |
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array_push($stack, $l + $r); |
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} elseif ($token === '-') { |
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array_push($stack, $l - $r); |
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} elseif ($token === '*') { |
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array_push($stack, $l * $r); |
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} else { |
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array_push($stack, (int)($l / $r)); |
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} |
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} |
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} |
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return array_pop($stack); |
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} |
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} |
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imajinyun /
leetcode-php
