kotlin go

Board.kt

    fun placeStone(player: Player, point: Point) {
        assert(isOnTheGrid(point))
        assert(isFree(point))

        //0. Examine the adjacent points.
        val adjacentSameColor = mutableSetOf<GoString>()
        val adjacentOppositeColor = mutableSetOf<GoString>()
        val liberties = mutableSetOf<Point>()

        for (neighbor in point.neighbors()) {
            if (!isOnTheGrid(neighbor))
                continue
            val neighborString = grid[neighbor]
            if (neighborString == null) {
                liberties.add(neighbor)
            } else if (neighborString.color == player) {
                adjacentSameColor.add(neighborString)
            } else {
                adjacentOppositeColor.add(neighborString)
            }
        }
        var newString = GoString(player, setOf(point), liberties)

        // 1. Merge any adjacent strings of the same color.
        for (sameColorString:GoString in adjacentSameColor) {
            newString = newString.mergeWith(sameColorString)
        }
        for (newStringPoint in newString.stones) {
            grid[newStringPoint] = newString
        }

        //2. Reduce liberties of any adjacent strings of the opposite color.
        for (otherColorString in adjacentOppositeColor) {
            otherColorString.removeLiberty(point)
        }

        //3. If any opposite color strings now have zero liberties, remove them.
        for (otherColorString in adjacentOppositeColor){
            if (otherColorString.liberties.size == 0) {
                removeString(otherColorString)
            }
        }

    }