38 lines
1.3 KiB
C++
38 lines
1.3 KiB
C++
// Compile with:
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// g++ -std=c++20 -Wall -Wextra -pedantic damm.cpp -o damm
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#include <iostream>
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#include <array> // for std::array
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#include <string> // for std::string, std::to_string and std::string::find
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const std::array<std::array<int, 10>, 10> table = {{ // Operation table
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{0, 3, 1, 7, 5, 9, 8, 6, 4, 2},
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{7, 0, 9, 2, 1, 5, 4, 8, 6, 3},
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{4, 2, 0, 6, 8, 7, 1, 3, 5, 9},
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{1, 7, 5, 0, 9, 8, 3, 4, 2, 6},
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{6, 1, 2, 3, 0, 4, 5, 9, 7, 8},
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{3, 6, 7, 4, 2, 0, 9, 5, 8, 1},
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{5, 8, 6, 9, 7, 2, 0, 1, 3, 4},
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{8, 9, 4, 5, 3, 6, 2, 0, 1, 7},
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{9, 4, 3, 8, 6, 1, 7, 2, 0, 5},
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{2, 5, 8, 1, 4, 3, 6, 7, 9, 0}
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}};
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bool damm(int input) {
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int interim = 0; // initialise to 0
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const std::string digit = "0123456789";
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for (const auto c : std::to_string(input))
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interim = table[interim][digit.find(c)];
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// Process the number digit by digit:
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// 1. The column index = number's digit
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// 2. The row index = interim digit
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// 3. Replace interim digit with table entry (table[<interim digit>][<number's digit>])
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return interim == 0; // Is interim digit equals zero? If so, the input is valid, invalid otherwise.
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}
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int main() {
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for (const auto num : {5724, 5727, 112946, 112949})
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std::cout << num << "\t" << "Checksum is " << (damm(num) ? "valid" : "invalid") << std::endl;
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return 0;
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}
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