32 lines
1.0 KiB
Markdown
32 lines
1.0 KiB
Markdown
---
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title: binomialCoefficient
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tags: math,algorithm,beginner
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firstSeen: 2018-02-14T12:34:02+02:00
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lastUpdated: 2020-12-28T13:49:24+02:00
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---
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Calculates the number of ways to choose `k` items from `n` items without repetition and without order.
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- Use `Number.isNaN()` to check if any of the two values is `NaN`.
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- Check if `k` is less than `0`, greater than or equal to `n`, equal to `1` or `n - 1` and return the appropriate result.
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- Check if `n - k` is less than `k` and switch their values accordingly.
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- Loop from `2` through `k` and calculate the binomial coefficient.
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- Use `Math.round()` to account for rounding errors in the calculation.
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```js
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const binomialCoefficient = (n, k) => {
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if (Number.isNaN(n) || Number.isNaN(k)) return NaN;
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if (k < 0 || k > n) return 0;
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if (k === 0 || k === n) return 1;
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if (k === 1 || k === n - 1) return n;
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if (n - k < k) k = n - k;
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let res = n;
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for (let j = 2; j <= k; j++) res *= (n - j + 1) / j;
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return Math.round(res);
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};
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```
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```js
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binomialCoefficient(8, 2); // 28
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```
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