num-of-islands

Number of Islands

https://leetcode.com/problems/number-of-islands/

Solution 1: DFS

if not grid:
    return 0
m, n = len(grid), len(grid[0])
 
def dfs(row, col) -> None:
    nonlocal grid, m, n
    if not (
        0 <= row < m and
        0 <= col < n and
        grid[row][col] == '1'
    ):
        return
    grid[row][col] = '0'
    dfs(row - 1, col)
    dfs(row + 1, col)
    dfs(row, col - 1)
    dfs(row, col + 1)
 
num_islands = 0
for row in range(m):
    for col in range(n):
        if grid[row][col] == "1":
            dfs(row, col)
            num_islands += 1
 
return num_islands

Solution 2: BFS

def bfs(row, col) -> None:
    nonlocal grid, m, n
    if not (
        0 <= row < m and
        0 <= col < n and
        grid[row][col] == '1'
    ):
        return
    grid[row][col] = '0'
    dfs(row - 1, col)
    dfs(row + 1, col)
    dfs(row, col - 1)
    dfs(row, col + 1)