# LeetCode 980. Unique Paths III in F#

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## URL

https://leetcode.com/problems/unique-paths-iii/

## Code

https://github.com/syohex/dotnet-study/blob/master/fsharp/leetcode/problems/0980/main.fsx

``````let uniquePaths3 (grid: int [,]) : int =
let mutable len = 0
let mutable start = 0, 0
let rows = Array2D.length1 grid
let cols = Array2D.length2 grid

for i in 0 .. (rows - 1) do
for j in 0 .. (cols - 1) do
if grid.[i, j] = 1 then start <- i, j
if grid.[i, j] <> -1 then len <- len + 1

let steps = [ (-1, 0); (0, -1); (1, 0); (0, 1) ]

let rec uniquePaths3' q (grid: int [,]) acc =
match q with
| [] -> acc
| ((row, col), visited) :: t ->
if grid.[row, col] = 2 then
if (visited |> Set.toList |> List.length) = len then
uniquePaths3' t grid (acc + 1)
else
uniquePaths3' t grid acc
else
let q' =
steps
|> List.map (fun (r, c) -> row + r, col + c)
|> List.filter (fun (r, c) ->
r >= 0
&& r < rows
&& c >= 0
&& c < cols
&& grid.[r, c] <> -1
&& (Set.contains (r, c) visited |> not))
|> List.fold (fun acc pos -> (pos, Set.add pos visited) :: acc) t

uniquePaths3' q' grid acc

let q = [ (start, Set.add start Set.empty) ]
uniquePaths3' q grid 0
``````