34 lines
698 B
PHP
34 lines
698 B
PHP
<?php
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$starting_numbers = explode(',', file_get_contents('input.txt'));
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$numbers = array_map('intval', $starting_numbers);
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$number = array_pop($numbers);
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for ($i = count($starting_numbers); $i <= 2020; $i++) {
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$number = newNumber($number);
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}
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echo $number;
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function newNumber(int $number = 0)
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{
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global $numbers;
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if (!in_array($number, $numbers, true)) {
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$numbers[] = $number;
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return $number;
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}
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$indexes = array_keys($numbers, $number);
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if (count($indexes) === 1) {
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$numbers[] = 0;
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return 0;
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}
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$new_number = $indexes[count($indexes) - 1] - $indexes[count($indexes) - 2];
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$numbers[] = $new_number;
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return $new_number;
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}
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