Leetcode 200 Number of Islands, leetcodeislands

Leetcode 200 Number of Islands, leetcodeislands

Given a 2d grid map'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

For any land found, find the land around which it can reach (the same land) and change its value (change it to 0 here) to prevent it from being recorded again. Note that the question is entered as a string array.

Here, conditions are set before the recursive method starts to prevent cross-border operations.

def num_islands(grid)  return 0 if not grid  ans = 0  grid.length.times do |i|    grid[0].length.times do |j|      if grid[i][j] == '1'        ans += 1        extend(grid,i,j)      end    end  end  ansenddef extend(grid,i,j)  if i<grid.length and j <grid[0].length and i>=0 and j>=0 and grid[i][j] == '1'    grid[i][j] = '0'    extend(grid,i+1,j)    extend(grid,i,j+1)    extend(grid,i-1,j)    extend(grid,i,j-1)  endend