It’s amusing just how similar our solutions are today. The only real issue I had today was not considering both sides of each range and only taking the last part of the range in the sort order.

var ingredientRanges: MutableList<LongRange> = mutableListOf()
var ingredients: MutableList<Long> = mutableListOf()

fun main() {
    val input = getInput(5)
    parseInput1(input)
    var count = 0L
    ingredientRanges.sortBy { it.first }
    var i = 0
    while (i < ingredientRanges.size) {
        var j = i + 1
        while (j < ingredientRanges.size && doRangesOverlap(ingredientRanges[i], ingredientRanges[j])) {
            ingredientRanges[i] = LongRange(ingredientRanges[i].first, max(ingredientRanges[i].last, ingredientRanges[j].last))
            j++
        }
        count += ingredientRanges[i].last - ingredientRanges[i].first + 1
        i = j
    }
    println(count)
}

fun parseInput1(input: String) {
    val split = input.split("\n\n")
    split[0].lines()
        .filter { it.isNotBlank() }
        .forEach {
            val range = it.split("-")
            ingredientRanges.add(LongRange(range[0].toLong(), range[1].toLong()))
        }
    split[1].lines()
        .filter { it.isNotBlank() }
        .forEach { ingredients.add(it.toLong()) }
}

fun doRangesOverlap(left: LongRange, right: LongRange): Boolean = right.first in left || right.first - 1 == left.last