def count_islands(grid):
    rows = len(grid)
    cols = len(grid[0]) if rows else 0
    seen = set()
    count = 0
    for r in range(rows):
        for c in range(cols):
            if grid[r][c] != 1 or (r, c) in seen:
                continue
            count += 1
            seen.add((r, c))
            stack = [(r, c)]
            while stack:
                x, y = stack.pop()
                for dx, dy in ((1,0),(-1,0),(0,1),(0,-1)):
                    nx, ny = x + dx, y + dy
                    if (0 <= nx < rows and 0 <= ny < cols
                            and grid[nx][ny] == 1 and (nx, ny) not in seen):
                        seen.add((nx, ny))
                        stack.append((nx, ny))
    return count