我有以下函数,它可以按照我想要的方式进行一次调用:
let shuffle (arr : 'a array) =
let array = Array.copy arr
let rng = new Random()
let n = array.Length
for x in 1..n do
let i = n-x
let j = rng.Next(i+1)
let tmp = array.[i]
array.[i] <- array.[j]
array.[j] <- tmp
array
但是,对于如下所示的多个调用(x 不用于任何内容),它会为每个调用生成相同的随机播放。如何让它每次产生不同的洗牌?
[for x in 1..3 do yield shuffle [|1;2;3|]]
>
val it : int [] list = [[|1; 3; 2|]; [|1; 3; 2|]; [|1; 3; 2|]]
你想像这样将随机移动到函数之外:
let rng = new Random()
let shuffle (arr : 'a array) =
let array = Array.copy arr
let n = array.Length
for x in 1..n do
let i = n-x
let j = rng.Next(i+1)
let tmp = array.[i]
array.[i] <- array.[j]
array.[j] <- tmp
array
原因是 RNG 默认按时间播种,在紧密循环中变化不够。 将 rng 移到函数之外意味着它会在调用中持续存在。