@technobuddha/library
Version:
A large library of useful functions
55 lines • 4.12 kB
JavaScript
import { create2dArray } from "./create2d-array.js";
/**
* Determine the longest possible array that is subsequence of both of given arrays.
* @remarks
* Implementation of [Longest Common Subsequence](https://en.wikipedia.org/wiki/Longest_common_subsequence) algorithm.
* @typeParam T - Type of objects in the arrays.
* @param array1 - First array of objects.
* @param array2 - Second array of objects.
* @param options - Functions to compare and collect elements from the two arrays
* @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.
* @example
* ```typescript
* longestCommonSubsequence(
* ['a', 'b', 'c', ' ', 'd', 'e', 'f'],
* ['a', 'c', ' ', 'd', 'e', 'c'],
* ); // ['a', 'c', ' ', 'd', 'e']
* ```
* @group Array
* @category Analysis
*/
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++) {
c[i][j] =
compare(array1[i - 1], array2[j - 1]) ?
c[i - 1][j - 1] + 1
: 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;
}
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