TopCoder SRM582: ColorTheCells

public class ColorTheCells {
    public int Dfs(int[] dryingTime, int[] paintTime, int pos = 0, int used = 0, int currentTime = 0) {
        int n = dryingTime.Length;
        if (used == (1 << n) - 1)
            return currentTime;
        int minTime = int.MaxValue;
        for (int movePos = 0; movePos < n; movePos++) {
            int dx = (pos <= movePos) ? 1 : -1;
            int p = pos;
            int time = currentTime;
            while (p != movePos) {
                time++;
                int nx = p + dx;
                if (((1 << nx) & used) != 0)
                    time = Math.Max(time, paintTime[nx] + dryingTime[nx] + 1);
                p = nx;
            }
            foreach (var paintPos in new[] { movePos - 1, movePos + 1 }) {
                if (0 <= paintPos && paintPos < n && ((1 << paintPos) & used) == 0) {
                    paintTime[paintPos] = time + 1;
                    minTime = Math.Min(minTime, Dfs(dryingTime, paintTime, movePos, used | (1 << paintPos), time + 1));
                    paintTime[paintPos] = 0;
                }
            }
        }
        return minTime;
    }

    public int minimalTime(int[] dryingTime) {
        int[] paintTime = new int[dryingTime.Length];
        return Dfs(dryingTime, paintTime);
    }