solutions/day4.fs


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namespace Solutions

module Day4 =
    open System.IO
    open System.Text.RegularExpressions

    type range = {
        startID: int;
        endID: int
    }

    let getRanges input =
        let matches = Regex.Matches(input, "(\d+)-(\d+),(\d+)-(\d+)") 
                        |> Seq.head 
                        |> fun x -> x.Groups 
                        |> Seq.map (fun x -> x.Value) 
                        |> List.ofSeq 
                        |> List.tail
        assert (Seq.length matches = 4)
        {startID = int matches[0]; endID = int matches[1]}, {startID = int matches[2]; endID = int matches[3]}
        
    let ranges = File.ReadLines("inputs/day4.txt") |> Seq.map getRanges

    let contains (rangeA, rangeB) =
        (rangeA.startID <= rangeB.startID && rangeA.endID >= rangeB.endID) || (rangeA.startID >= rangeB.startID && rangeA.endID <= rangeB.endID)

    let part1 () = ranges |> Seq.filter contains |> Seq.length

    let overlaps (rangeA, rangeB) =
        (rangeA.startID >= rangeB.startID && rangeA.startID <= rangeB.endID) ||
        (rangeA.endID >= rangeB.startID && rangeA.endID <= rangeB.endID)     ||
        (rangeB.startID >= rangeA.startID && rangeB.startID <= rangeA.endID) ||
        (rangeB.endID >= rangeA.startID && rangeB.endID <= rangeA.endID)
    
    let part2 () = ranges |> Seq.filter overlaps |> Seq.length