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:
Input:
11110
11010
11000
00000
Output: 1
Example 2:
Input:
11000
11000
00100
00011
Output: 3
Solution
Use DFS to check which island each point belongs.
class Solution {
func numIslands(_ grid: [[Character]]) -> Int {
var grid = grid
var res = 0
for i in 0..<grid.count {
for j in 0..<grid[0].count {
if grid[i][j] == "1" {
res += 1
dfs(&grid, i, j)
}
}
}
return res
}
func dfs(_ grid: inout [[Character]], _ row: Int, _ col: Int) {
if row < 0 || col < 0 || row >= grid.count || col >= grid[0].count { return }
if grid[row][col] != "1" { return }
grid[row][col] = "x" //mark visited
dfs(&grid, row, col + 1)
dfs(&grid, row, col - 1)
dfs(&grid, row, col - 1)
dfs(&grid, row - 1, col)
dfs(&grid, row + 1, col)
}
}