48 lines
953 B
PHP
48 lines
953 B
PHP
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<?php
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$ids = explode("\n", file_get_contents('input.txt'));
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//$ids = ['FBFBBFFRLR'];
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$max_seat_id = 0;
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function decodeRow($row)
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{
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$min = 1;
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$max = 128;
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foreach (str_split($row) as $cell) {
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if ($cell === 'F') {
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$max = floor($min + ($max - $min) / 2);
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} else {
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$min = ceil($max - ($max - $min) / 2);
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}
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}
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return $min - 1;
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}
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function decodeColumn($column)
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{
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$min = 1;
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$max = 8;
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foreach (str_split($column) as $cell) {
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if ($cell === 'L') {
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$max = floor($min + ($max - $min) / 2);
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} else {
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$min = ceil($max - ($max - $min) / 2);
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}
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}
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return $min - 1;
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}
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foreach ($ids as $id) {
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$encoded_row = substr($id, 0, 7);
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$encoded_column = substr($id, 7);
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$row = decodeRow($encoded_row);
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$column = decodeColumn($encoded_column);
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$max_seat_id = max($max_seat_id, ($row * 8 + $column));
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}
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echo $max_seat_id;
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