given a 2d grid map of 1 s land and 0 s water count the number of islands an island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically you may assume all four edges of the grid are all surrounded by water example 1 11110 11010 11000 00000 answer 1 example 2 11000 11000 00100 00011 answer 3
def num_islands(grid):
    count = 0
    for i in range(len(grid)):
        for j, col in enumerate(grid[i]):
            if col == 1:
                dfs(grid, i, j)
                count += 1
    return count


def dfs(grid, i, j):
    if (i < 0 or i >= len(grid)) or (j < 0 or j >= len(grid[0])):
        return
    if grid[i][j] != 1:
        return
    grid[i][j] = 0
    dfs(grid, i+1, j)
    dfs(grid, i-1, j)
    dfs(grid, i, j+1)
    dfs(grid, i, j-1)