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Pascal's Triangle (2)

This code sample generates Pascal's triangle as jagged 2D list (list of lists). It takes 0.5 sec to generate 3000 rows (vs 16 sec for http://fssnip.net/23). Tip: try to avoid of using "list1 @ list2" construction. 

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let pascal n = 
  let rec nextrow row y ys =
    match row with
    | x::xs -> nextrow xs x ((x + y)::ys)
    | [] -> 1::ys
  let rec addrow i z zs = 
    if i <= 1 then z::zs
    else addrow (i-1) (nextrow z 0 []) (z::zs)
  addrow n [1] []
val pascal : n:int -> int list list

Full name: Script.pascal
val n : int
val nextrow : (int list -> int -> int list -> int list)
val row : int list
val y : int
val ys : int list
val x : int
val xs : int list
val addrow : (int -> int list -> int list list -> int list list)
val i : int
val z : int list
val zs : int list list
Raw view Test code New version

More information

Link:http://fssnip.net/2b
Posted:13 years ago
Author:Shamil Sayfutdinov
Tags: lists , jagged array , algorithms , learning f#

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The first version of fssnip.net has been created by @tomaspetricek back in 2010. This web site is a new, open-source and contribution-friendly version.