Số lượng đảo

def num_islands_opt(grid: list[list[str]]) -> int:
    if not grid: return 0
    rows, cols = len(grid), len(grid[0])
    islands = 0
    def dfs(r, c):
        if r < 0 or c < 0 or r >= rows or c >= cols or grid[r][c] == "0":
            return
        grid[r][c] = "0"
        dfs(r + 1, c)
        dfs(r - 1, c)
        dfs(r, c + 1)
        dfs(r, c - 1)
    for r in range(rows):
        for c in range(cols):
            if grid[r][c] == "1":
                dfs(r, c)
                islands += 1
    return islands

def num_islands_brute(grid: list[list[str]]) -> int:
    if not grid: return 0
    rows, cols = len(grid), len(grid[0])
    visited = set()
    islands = 0
    def bfs(r, c):
        q = [(r, c)]
        visited.add((r, c))
        while q:
            row, col = q.pop(0)
            directions = [[1,0], [-1,0], [0,1], [0,-1]]
            for dr, dc in directions:
                nr, nc = row + dr, col + dc
                if 0 <= nr < rows and 0 <= nc < cols and grid[nr][nc] == "1" and (nr, nc) not in visited:
                    q.append((nr, nc))
                    visited.add((nr, nc))
    for r in range(rows):
        for c in range(cols):
            if grid[r][c] == "1" and (r, c) not in visited:
                bfs(r, c)
                islands += 1
    return islands