TopCoder SRM578: GooseInZooDivTwo

public class GooseInZooDivTwo {
    public int count(string[] field, int dist) {
        int w = field[0].Length;
        int h = field.Length;
        int mod = 1000000007;
        var points =
            from i in Enumerable.Range(0, h)
            from j in Enumerable.Range(0, w)
            where field[i][j] == 'v'
            select new { r = i, c = j, id = i * w + j };

        DisjointSet set = new DisjointSet(w * h);

        int groupNum = points.Count();
        if (groupNum == 0) return 0;

        foreach (var p1 in points) {
            foreach (var p2 in points) {
                int d = Math.Abs(p1.c - p2.c) + Math.Abs(p1.r - p2.r);
                if (d <= dist) {
                    if (!set.isSameSet(p1.id, p2.id)) {
                        set.unionSet(p1.id, p2.id);
                        groupNum--;
                    }
                }
            }
        }

        int ans = 1;
        for (int i = 0; i < groupNum; i++) {
            ans = (ans * 2) % mod;
        }
        return (ans + mod - 1) % mod;
    }
}