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@rjyo
Last active May 12, 2020 11:55
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/**
* 一次挑选的不重复几率
*
* @param n 总种类数
* @param m 第m次挑选
* @param batch 每次选的本数,默认为3
*/
const op = (n: number, m = 0, batch = 3) => {
const s = n - batch * m
return (s / n) * ((s - 1) / (n - 1)) * ((s - 2) / (n - 2))
}
/**
* 挑选m次后的不重复几率
*
* @param n 总种类数
* @param m 挑选次数
*/
const f = (n: number, m: number) => {
let rv = 1
for (let i = 0; i < m; i++) rv *= op(n, i)
return rv
}
console.log(f(100, 1)) // 1
console.log(f(5000, 12)) // 0.8877207442529191
console.log(f(1000, 12)) // 0.5479560754243109
console.log(f(500, 12)) // 0.2955830495139548
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