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Add Luhn Algorithm.
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| /* | ||
| * MIT License | ||
| * | ||
| * Copyright (c) 2017-2019 Ilkka Seppälä | ||
| * | ||
| * Permission is hereby granted, free of charge, to any person obtaining a copy | ||
| * of this software and associated documentation files (the "Software"), to deal | ||
| * in the Software without restriction, including without limitation the rights | ||
| * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell | ||
| * copies of the Software, and to permit persons to whom the Software is | ||
| * furnished to do so, subject to the following conditions: | ||
| * | ||
| * The above copyright notice and this permission notice shall be included in all | ||
| * copies or substantial portions of the Software. | ||
| * | ||
| * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR | ||
| * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, | ||
| * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE | ||
| * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER | ||
| * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, | ||
| * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE | ||
| * SOFTWARE. | ||
| */ | ||
|
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| package math; | ||
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| public class LuhnSnippet { | ||
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| /** | ||
| * Calculates checksum for a given number with Luhn's algorithm. Works only on non-negative | ||
| * integers not greater than {@link Long#MAX_VALUE} i.e., all numbers with a maximum of 18 | ||
| * digits, plus 19-digit-long numbers start with 1..8 (also some with 9, too). For | ||
| * demonstration purposes, algorithm is not optimized for efficiency. | ||
| * | ||
| * @param num number whose checksum is to be calculated | ||
| * @return checksum value for num | ||
| * @see <a href="https://patents.google.com/patent/US2950048A">Hans P. LUHN's patent US2950048A</a> | ||
| * @see <a href="https://en.wikipedia.org/wiki/Luhn_algorithm">Luhn algorithm on Wikipedia</a> | ||
| */ | ||
| public static int calculateLuhnChecksum(long num) { | ||
| if (num < 0) { | ||
| throw new IllegalArgumentException("Non-negative numbers only."); | ||
| } | ||
| final var numStr = String.valueOf(num); | ||
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| var sum = 0; | ||
| var isOddPosition = true; | ||
| // Loop on digits of numStr from right to left. | ||
| for (var i = numStr.length() - 1; i >= 0; i--) { | ||
| final var digit = Integer.parseInt(Character.toString(numStr.charAt(i))); | ||
| final var substituteDigit = (isOddPosition ? 2 : 1) * digit; | ||
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| final var tensPlaceDigit = substituteDigit / 10; | ||
| final var onesPlaceDigit = substituteDigit % 10; | ||
| sum += tensPlaceDigit + onesPlaceDigit; | ||
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| isOddPosition = !isOddPosition; | ||
| } | ||
| final var checksumDigit = (10 - (sum % 10)) % 10; | ||
| // Outermost modulus handles edge case `num = 0`. | ||
| return checksumDigit; | ||
| } | ||
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| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,90 @@ | ||
| /* | ||
| * MIT License | ||
| * | ||
| * Copyright (c) 2017-2019 Ilkka Seppälä | ||
| * | ||
| * Permission is hereby granted, free of charge, to any person obtaining a copy | ||
| * of this software and associated documentation files (the "Software"), to deal | ||
| * in the Software without restriction, including without limitation the rights | ||
| * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell | ||
| * copies of the Software, and to permit persons to whom the Software is | ||
| * furnished to do so, subject to the following conditions: | ||
| * | ||
| * The above copyright notice and this permission notice shall be included in all | ||
| * copies or substantial portions of the Software. | ||
| * | ||
| * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR | ||
| * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, | ||
| * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE | ||
| * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER | ||
| * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, | ||
| * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE | ||
| * SOFTWARE. | ||
| */ | ||
|
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| package math; | ||
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| import static org.junit.jupiter.api.Assertions.assertEquals; | ||
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| import org.junit.jupiter.params.ParameterizedTest; | ||
| import org.junit.jupiter.params.provider.CsvSource; | ||
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| class LuhnSnippetTest { | ||
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| @CsvSource({ | ||
| "0, 0", | ||
| "1, 8", | ||
| "4, 2", | ||
| "5, 9", | ||
| "9, 1", | ||
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| "42, 2", | ||
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| // Moderately interesting patterns. | ||
| "10, 9", | ||
| "11, 7", | ||
| "12, 5", | ||
| "100, 8", | ||
| "101, 6", | ||
| "102, 4", | ||
| "1000, 9", | ||
| "1001, 7", | ||
| "1002, 5", | ||
| "10000, 8", | ||
| "10001, 6", | ||
| "10002, 4", // etc. | ||
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| // Can detect any single-digit error. | ||
| "4872148, 4", // Original number (Luhn's example in patent US2950048A). | ||
| "4872143, 5", | ||
| // ^ | ||
| "4872178, 1", | ||
| // ^ | ||
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| // Can detect many transposition of adjacent digits. | ||
| "4872418, 1", | ||
| // ^^ | ||
| "4872184, 9", | ||
| // ^^ | ||
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| // Can not detect some transposition of adjacent digits. | ||
| "109223344, 2", // Original number. | ||
| "190223344, 2", // 09<-->90 | ||
| //^^ | ||
| "109553344, 2", // 22<-->55 | ||
| // ^^ | ||
| "109226644, 2", // 33<-->66 | ||
| // ^^ | ||
| "109223377, 2", // 44<-->77 | ||
| // ^^ | ||
| "190226644, 2", // Some of the above together. | ||
| //^^ ^^ | ||
| "190556677, 2", // All of the above together. | ||
| //^^^^^^^^ | ||
| }) | ||
| @ParameterizedTest | ||
| void testLuhnCalculateChecksum(long num, int expectedChecksum) { | ||
| assertEquals(expectedChecksum, LuhnSnippet.calculateLuhnChecksum(num)); | ||
| } | ||
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| } |