A solution to the flood-fill related question described here: https://youtu.be/IWvbPIYQPFM

countMaxFloodFill.kt

fun countMaxFloodFill(colors: Array<IntArray>): Int {
    var best = 0

    val counts = arrayOfNulls<AtomicInteger?>(colors.size)
    
    colors.forEachIndexed { y, rows ->
        rows.forEachIndexed { x, color ->
            // get the current count from the neighbour above or to the left of the current cell if either have the same color.
            // If above and left have the same color, check if they are connected, if they are not, we can connect them and add them together.
            val leftIsSameColor = colors.getOrNull(y)?.getOrNull(x - 1)
            val aboveIsSameColor = colors.getOrNull(y - 1)?.getOrNull(x)
            val intRef = when {
                leftIsSameColor && aboveIsSameColor -> {
                    if(counts[x - 1] !== counts[x]) {
                        counts[x].addAndGet(counts[x - 1].get())
                        counts[x - 1] = counts[x]
                        counts[x]
                    } else {
                        if(counts[x] > counts[x - 1]) counts[x] else counts[x - 1]
                    }
                }
                leftIsSameColor -> counts[x - 1]
                aboveIsSameColor -> counts[x]
                else -> null
            }
            // Increment it or if this is a new region set it to 1.
            best = intRef?.incrementAndGet() ?: 1
            counts[x] = intRef ?: AtomicInteger(1)
        }
    }

    return best
}