aureooms-js-array/lib/map/permutations.js

array manipulation code bricks for JavaScript

'use strict';

Object.defineProperty(exports, "__esModule", {
	value: true
});
exports.permutations = permutations;

var _ = require('..');

function permutations(iterable, repeat, out) {

	// permutations('ABCD', 2) --> AB AC AD BA BC BD CA CB CD DA DB DC
	// permutations(range(3), 3) --> 012 021 102 120 201 210

	var pool, i, j, w, len, indices, cycles, x, tmp;

	pool = iterable;
	len = pool.length;

	if (repeat > len) {
		return out;
	}

	indices = (0, _.range)(0, len, 1, []);
	cycles = (0, _.range)(len, len - repeat, -1, []);

	out.push((0, _.pick)(pool, indices.slice(0, repeat), []));

	if (repeat === 0 || len === 0) {
		return out;
	}

	for (;;) {

		i = repeat;

		while (i--) {

			--cycles[i];

			if (cycles[i] === 0) {

				x = indices[i];

				indices.splice(i, 1);
				indices.push(x);

				cycles[i] = len - i;
			} else {

				j = cycles[i];

				tmp = indices[i];
				indices[i] = indices[len - j];
				indices[len - j] = tmp;

				out.push((0, _.pick)(pool, indices.slice(0, repeat), []));
				break;
			}
		}

		if (i === -1) {
			return out;
		}
	}
}
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