74 lines
2.0 KiB
JavaScript
74 lines
2.0 KiB
JavaScript
|
import { factory } from '../../utils/factory.js';
|
||
|
|
import { combinationsNumber } from '../../plain/number/combinations.js';
|
||
|
|
var name = 'combinations';
|
||
|
|
var dependencies = ['typed'];
|
||
|
|
export var createCombinations = /* #__PURE__ */factory(name, dependencies, _ref => {
|
||
|
|
var {
|
||
|
|
typed
|
||
|
|
} = _ref;
|
||
|
|
|
||
|
|
/**
|
||
|
|
* Compute the number of ways of picking `k` unordered outcomes from `n`
|
||
|
|
* possibilities.
|
||
|
|
*
|
||
|
|
* Combinations only takes integer arguments.
|
||
|
|
* The following condition must be enforced: k <= n.
|
||
|
|
*
|
||
|
|
* Syntax:
|
||
|
|
*
|
||
|
|
* math.combinations(n, k)
|
||
|
|
*
|
||
|
|
* Examples:
|
||
|
|
*
|
||
|
|
* math.combinations(7, 5) // returns 21
|
||
|
|
*
|
||
|
|
* See also:
|
||
|
|
*
|
||
|
|
* combinationsWithRep, permutations, factorial
|
||
|
|
*
|
||
|
|
* @param {number | BigNumber} n Total number of objects in the set
|
||
|
|
* @param {number | BigNumber} k Number of objects in the subset
|
||
|
|
* @return {number | BigNumber} Number of possible combinations.
|
||
|
|
*/
|
||
|
|
return typed(name, {
|
||
|
|
'number, number': combinationsNumber,
|
||
|
|
'BigNumber, BigNumber': function BigNumberBigNumber(n, k) {
|
||
|
|
var BigNumber = n.constructor;
|
||
|
|
var result, i;
|
||
|
|
var nMinusk = n.minus(k);
|
||
|
|
var one = new BigNumber(1);
|
||
|
|
|
||
|
|
if (!isPositiveInteger(n) || !isPositiveInteger(k)) {
|
||
|
|
throw new TypeError('Positive integer value expected in function combinations');
|
||
|
|
}
|
||
|
|
|
||
|
|
if (k.gt(n)) {
|
||
|
|
throw new TypeError('k must be less than n in function combinations');
|
||
|
|
}
|
||
|
|
|
||
|
|
result = one;
|
||
|
|
|
||
|
|
if (k.lt(nMinusk)) {
|
||
|
|
for (i = one; i.lte(nMinusk); i = i.plus(one)) {
|
||
|
|
result = result.times(k.plus(i)).dividedBy(i);
|
||
|
|
}
|
||
|
|
} else {
|
||
|
|
for (i = one; i.lte(k); i = i.plus(one)) {
|
||
|
|
result = result.times(nMinusk.plus(i)).dividedBy(i);
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
return result;
|
||
|
|
} // TODO: implement support for collection in combinations
|
||
|
|
|
||
|
|
});
|
||
|
|
});
|
||
|
|
/**
|
||
|
|
* Test whether BigNumber n is a positive integer
|
||
|
|
* @param {BigNumber} n
|
||
|
|
* @returns {boolean} isPositiveInteger
|
||
|
|
*/
|
||
|
|
|
||
|
|
function isPositiveInteger(n) {
|
||
|
|
return n.isInteger() && n.gte(0);
|
||
|
|
}
|