Pattern - Grid Components

You solved "Number of Islands" with DFS. But DSU works for grids too, especially if you flip pixels from Water to Land dynamically.

Map each cell $(r, c)$ to a $1D$ index: id = r * cols + c. Initialize DSU with all land cells. For each land cell, union with adjacent land cells (up, down, left, right).

id := row * numCols + col
if grid[row][col] = Land
    for each neighbor (nr, nc)
        if grid[nr][nc] = Land
            union(id, nr * numCols + nc)

DSU shines when land cells appear one at a time (dynamic connectivity). With DFS, you would need to re-run from scratch each time.