Evaluates the binomial coefficient of two integers n
and k
.
Use Number.isNaN()
to check if any of the two values is NaN
.
Check if k
is less than 0
, greater than or equal to n
, equal to 1
or n - 1
and return the appropriate result.
Check if n - k
is less than k
and switch their values accordingly.
Loop from 2
through k
and calculate the binomial coefficient.
Use Math.round()
to account for rounding errors in the calculation.
代码片段
const binomialCoefficient = (n, k) => {
if (Number.isNaN(n) || Number.isNaN(k)) return NaN;
if (k < 0 || k > n) return 0;
if (k === 0 || k === n) return 1;
if (k === 1 || k === n - 1) return n;
if (n - k < k) k = n - k;
let res = n;
for (let j = 2; j <= k; j++) res *= (n - j + 1) / j;
return Math.round(res);
};
使用样例
binomialCoefficient(8, 2); // 28