@extra-array/is-subsequence/searchSubsequence.js

Checks if array has a subsequence.

import id from './_id';
import cmp from './_cmp';
/**
 * Finds first index of a subsequence.
 * @param x an array
 * @param y subsequence?
 * @param fc compare function (a, b)
 * @param fm map function (v, i, x)
 */
function searchSubsequence(x, y, fc = null, fm = null) {
    var fc = fc || cmp, fm = fm || id;
    var y1 = [...y].map(fm), Y = y1.length;
    var a = -1, i = -1, j = 0;
    for (var u of x) {
        var u1 = fm(u, ++i, x);
        if (fc(u1, y1[j]) !== 0)
            continue;
        if (a < 0)
            a = i;
        if (++j >= Y)
            return a;
    }
    return -1;
}
export default searchSubsequence;
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