DFS&BFS - 200. Number of Islands

200. Number of Islands

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

思路：

题目意思是在一个二维平面找出有多少个岛屿，可以使用dfs或者bfs做，这里使用dfs来做，每找到一个点是岛屿，就不断四个方向探索，把探索过的区域打上标记或者置为水域就可以。

代码：

go：

var dirs = [][]int{{-1, 0},{1, 0}, {0, -1}, {0, 1}}


func numIslands(grid [][]byte) int {
    var res int
    //sanity check
    if grid == nil || len(grid) == 0 || len(grid[0]) == 0 {
        return res
    }
    
    row, col := len(grid), len(grid[0])
    for i := 0; i < row; i++ {
        for j := 0; j < col; j++ {
            if grid[i][j] == '1' {
                res++
                dfs(&grid, i, j, row, col)
            }
        }
    }
    
    return res
}

func dfs(grid *[][]byte, x, y int, row, col int) {
    // base case
    if x < 0 || x >= row || y < 0 || y >= col || (*grid)[x][y] == '0' || (*grid)[x][y] == '2' {
        return 
    }
    
    (*grid)[x][y] = '2'
    for _, dir := range dirs {
        dfs(grid, dir[0] + x, dir[1] + y, row, col)
    }
}