public int NumIslands(char[][] grid)
{
int rows = grid.Length;
if (rows == 0)
{
return(0);
}
int cols = grid[0].Length;
if (cols == 0)
{
return(0);
}
int n = rows * cols;
UnionSet uset = new UnionSet(n);
for (int row = 0; row < rows; row++)
{
int index = row * cols;
for (int col = 0; col < cols; col++)
{
if (grid[row][col] == '1')
{
if (row > 0 && grid[row - 1][col] == '1')
{
uset.Union(index + col, index - cols + col);
}
if (col > 0 && grid[row][col - 1] == '1')
{
uset.Union(index + col, index + col - 1);
}
}
}
}
HashSet <int> count = new HashSet <int>();
for (int row = 0; row < rows; row++)
{
int index = row * cols;
for (int col = 0; col < cols; col++)
{
if (grid[row][col] == '1')
{
count.Add(uset.Find(index + col));
}
}
}
return(count.Count);
}
