namespace AdventOfCode2023

open System

[<RequireQualifiedAccess>]
module Day11 =

    let inline private toRowAndCol (lineLength : int) (pos : int) : struct (int * int) =
        let lineNum = pos / lineLength
        let withinLine = pos % lineLength
        struct (lineNum, withinLine)

    let inline private ofRowAndCol (lineLength : int) (lineNum : int) (col : int) : int = lineNum * lineLength + col

    let part1 (s : string) =
        let galaxies = ResizeArray ()
        let rowsWithoutGalaxies = ResizeArray ()
        let rowLength = s.IndexOf '\n'
        let mutable hasAnyGalaxy = false
        let mutable currRowIndex = 0
        let mutable currColIndex = 0

        for c in s do
            if c = '\n' then
                if not hasAnyGalaxy then
                    rowsWithoutGalaxies.Add currRowIndex

                currRowIndex <- currRowIndex + 1
                currColIndex <- 0
                hasAnyGalaxy <- false
            elif c = '#' then
                hasAnyGalaxy <- true
                galaxies.Add (currRowIndex, currColIndex)
                currColIndex <- currColIndex + 1
            else
                currColIndex <- currColIndex + 1

        galaxies.Sort (fun (_, c1) (_, c2) -> compare c1 c2)

        let colsWithoutGalaxies =
            let result = ResizeArray ()
            let mutable prevCol = 0

            for (_, c) in galaxies do
                if c > prevCol then
                    for j = prevCol + 1 to c - 1 do
                        result.Add j

                    prevCol <- c

            result

        let mutable answer = 0

        for galaxy1 = 0 to galaxies.Count - 1 do
            let row1, col1 = galaxies.[galaxy1]

            for galaxy2 = galaxy1 + 1 to galaxies.Count - 1 do
                let row2, col2 = galaxies.[galaxy2]
                let baseDistance = abs (row1 - row2) + abs (col1 - col2)

                let extraDistance =
                    let mutable extraDistance = 0

                    for i = 1 + min row1 row2 to max row1 row2 - 1 do
                        if rowsWithoutGalaxies.Contains i then
                            extraDistance <- extraDistance + 1

                    for i = 1 + min col1 col2 to max col1 col2 - 1 do
                        if colsWithoutGalaxies.Contains i then
                            extraDistance <- extraDistance + 1

                    extraDistance

                answer <- answer + extraDistance + baseDistance

        answer

    let part2 (s : string) =
        use s = StringSplitEnumerator.make '\n' s
        0