@extra-array/is-permutation/index.js

Checks if array has a permutation.

'use strict';

/**
 * Gives same value.
 * @param v a value
 * @returns v
 */
function id(v) {
    return v;
}

/**
 * Compares two values.
 * @param a a value
 * @param b another value
 * @returns a<b: -1, a=b: 0, a>b: 1
 */
function cmp(a, b) {
    return a < b ? -1 : (a > b ? 1 : 0);
}

/**
 * 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;
}

/**
 * Checks if array has a subsequence.
 * @param x an array
 * @param y subsequence?
 * @param fc compare function (a, b)
 * @param fm map function (v, i, x)
 */
function isSubsequence(x, y, fc = null, fm = null) {
    return searchSubsequence(x, y, fc, fm) >= 0;
}

/**
 * Checks if array has a permutation.
 * @param x an array
 * @param y permutation?
 * @param fc map function (v, i, x)
 * @param fm compare function (a, b)
 */
function isPermutation(x, y, fc = null, fm = null) {
    var x1 = fm ? x.map(fm) : x.slice();
    var y1 = fm ? y.map(fm) : y.slice();
    return isSubsequence(x1.sort(), y1.sort(), fc, fm);
}

module.exports = isPermutation;