Leetcode min deletions https://leetcode.com/problems/minimum-deletions-to-make-character-frequencies-unique/

min.fs

let rec min count counts = 
    if count = 0 then 0
    else if not (List.contains count counts) then
        0
    else 
        1 +  min (count - 1) counts

let minDeletions (str : string) = 
    let step m elem  = 
        if Map.containsKey elem m then 
            m |> Map.map (fun key value -> if key = elem then value + 1 else value)
        else m |> Map.add elem 1 
    let counts = [ for s in str do s ] |> List.fold step Map.empty |> Map.toList |> List.map snd 
    let rec countDeletions l = 
        match l with 
        | [] -> (0, [])
        | x :: xs -> 
            let count, xs = countDeletions xs
            let m = min x xs  
            (m+count,x-m :: xs)
    in 
    counts |> countDeletions |> fst