@technobuddha/library/longestCommonSubsequence/longestCommonSubsequence.mjs

A large library of useful functions

import create2DArray from '../create2DArray';
/**
 * Implementation of Longest Common Subsequence problem.
 * http://en.wikipedia.org/wiki/Longest_common_subsequence
 *
 * Returns the longest possible array that is subarray of both of given arrays.
 *
 * @param array1 First array of objects.
 * @param array2 Second array of objects.
 * @param __namedParameters see {@link Options}
 * @default compare equality comparison
 * @default collect basic collector
 * @returns A list of objects that are common to both arrays
 * such that there is no common subsequence with size greater than the
 * length of the list.
 */
export function longestCommonSubsequence(array1, array2, { compare = (a, b) => a === b, collect = (i1, _i2) => array1[i1] } = {}) {
    const l1 = array1.length;
    const l2 = array2.length;
    const c = create2DArray(l1 + 1, l2 + 1, 0);
    let i;
    let j;
    for (i = 1; i <= l1; i++) {
        for (j = 1; j <= l2; j++) {
            if (compare(array1[i - 1], array2[j - 1]))
                c[i][j] = c[i - 1][j - 1] + 1;
            else
                c[i][j] = Math.max(c[i - 1][j], c[i][j - 1]);
        }
    }
    const result = [];
    i = l1;
    j = l2;
    while (i > 0 && j > 0) {
        if (compare(array1[i - 1], array2[j - 1])) {
            result.unshift(collect(i - 1, j - 1));
            i--;
            j--;
        }
        else if (c[i - 1][j] > c[i][j - 1]) {
            i--;
        }
        else {
            j--;
        }
    }
    return result;
}
export default longestCommonSubsequence;