verhoeff-algorithm/index.ts

A TypeScript implementation of the Verhoeff algorithm.

const multiplicationTable: number[][] = [
  [0, 1, 2, 3, 4, 5, 6, 7, 8, 9],
  [1, 2, 3, 4, 0, 6, 7, 8, 9, 5],
  [2, 3, 4, 0, 1, 7, 8, 9, 5, 6],
  [3, 4, 0, 1, 2, 8, 9, 5, 6, 7],
  [4, 0, 1, 2, 3, 9, 5, 6, 7, 8],
  [5, 9, 8, 7, 6, 0, 4, 3, 2, 1],
  [6, 5, 9, 8, 7, 1, 0, 4, 3, 2],
  [7, 6, 5, 9, 8, 2, 1, 0, 4, 3],
  [8, 7, 6, 5, 9, 3, 2, 1, 0, 4],
  [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
];

const permutationTable: number[][] = [
  [0, 1, 2, 3, 4, 5, 6, 7, 8, 9],
  [1, 5, 7, 6, 2, 8, 3, 0, 9, 4],
  [5, 8, 0, 3, 7, 9, 6, 1, 4, 2],
  [8, 9, 1, 6, 0, 4, 3, 5, 2, 7],
  [9, 4, 5, 3, 1, 2, 6, 8, 7, 0],
  [4, 2, 8, 6, 5, 7, 3, 9, 0, 1],
  [2, 7, 9, 3, 8, 0, 6, 4, 1, 5],
  [7, 0, 4, 6, 9, 1, 3, 2, 5, 8]
];

/**
* Calculates the Verhoeff checksum for a given number array.
* @param numberArray An array of digits representing the number.
* @returns The checksum value.
*/
function calculateChecksum(numberArray: number[]): number {
  let c = 0;
  const invertedArray = numberArray.slice().reverse();

  invertedArray.forEach((val, i) => {
    c = multiplicationTable[c][permutationTable[i % 8][val]];
  });

  return c;
}

/**
* Validates if the given number passes the Verhoeff check.
* @param number A string representing the number to check.
* @returns A boolean indicating if the number is valid.
*/
export function isValidVerhoeff(number: string): boolean {
  const numberArray: number[] = number.split("").map(Number);
  return calculateChecksum(numberArray) === 0;
}