39 lines
1.4 KiB
JavaScript
39 lines
1.4 KiB
JavaScript
"use strict";
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Object.defineProperty(exports, "__esModule", {
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value: true
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});
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exports.combinationsNumber = combinationsNumber;
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var _number = require("../../utils/number.js");
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var _product = require("../../utils/product.js");
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function combinationsNumber(n, k) {
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if (!(0, _number.isInteger)(n) || n < 0) {
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throw new TypeError('Positive integer value expected in function combinations');
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}
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if (!(0, _number.isInteger)(k) || k < 0) {
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throw new TypeError('Positive integer value expected in function combinations');
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}
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if (k > n) {
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throw new TypeError('k must be less than or equal to n');
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}
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const nMinusk = n - k;
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let answer = 1;
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const firstnumerator = k < nMinusk ? nMinusk + 1 : k + 1;
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let nextdivisor = 2;
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const lastdivisor = k < nMinusk ? k : nMinusk;
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// balance multiplications and divisions to try to keep intermediate values
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// in exact-integer range as long as possible
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for (let nextnumerator = firstnumerator; nextnumerator <= n; ++nextnumerator) {
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answer *= nextnumerator;
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while (nextdivisor <= lastdivisor && answer % nextdivisor === 0) {
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answer /= nextdivisor;
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++nextdivisor;
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}
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}
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// for big n, k, floating point may have caused weirdness in remainder
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if (nextdivisor <= lastdivisor) {
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answer /= (0, _product.product)(nextdivisor, lastdivisor);
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}
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return answer;
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}
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combinationsNumber.signature = 'number, number'; |