200. 岛屿数量

func numIslands(grid [][]byte) int {
    n := len(grid)
    if n == 0{
        return 0
    }
    //初始全部未访问过 false。注意二： 给的是一个n*m数组，而不是n*n数组
    flag := make([][]bool,n)
    m := len(grid[0])
    for i:=0;i<n;i++{
        flag[i] = make([]bool,m)
    }
    res := 0
    for i:=0;i<n;i++{
        for j:=0;j<m;j++{
            if flag[i][j] == false && grid[i][j] == ‘1‘{
                dfs(flag,grid,n,m,i,j)
                res++
            }
        }
    }
    return res
}
//注意一 不是else逻辑。
func dfs(flag [][]bool,grid [][]byte, n,m ,i,j int) {
    if flag[i][j] == false && grid[i][j] == ‘1‘{
        flag[i][j] = true
        if i-1 >=0{
            dfs(flag,grid,n,m,i-1,j)
        }
        if i+1 <n{
            dfs(flag,grid,n,m,i+1,j)
        } 
        if j-1>=0{
            dfs(flag,grid,n,m,i,j-1)
        } 
        if j+1<m{
            dfs(flag,grid,n,m,i,j+1)
        }
    }
    return 
}

func numIslands(grid [][]byte) int {
    n := len(grid)
    if n == 0{
        return 0
    }
    m := len(grid[0])
    res := 0
    for i:=0;i<n;i++{
        for j:=0;j<m;j++{
            if  grid[i][j] == ‘1‘{
                dfs(grid,n,m,i,j)
                res++
            }
        }
    }
    return res
}
//注意一 不是else逻辑。
func dfs(grid [][]byte, n,m ,i,j int) {
    if  grid[i][j] == ‘1‘{
        grid[i][j] = ‘0‘
        if i-1 >=0{
            dfs(grid,n,m,i-1,j)
        }
        if i+1 <n{
            dfs(grid,n,m,i+1,j)
        } 
        if j-1>=0{
            dfs(grid,n,m,i,j-1)
        } 
        if j+1<m{
            dfs(grid,n,m,i,j+1)
        }
    }
    return 
}

func numIslands(grid [][]byte) int {
    n := len(grid)
    if n == 0{
        return 0
    }
    m := len(grid[0])
    res := 0
    for i:=0;i<n;i++{
        for j:=0;j<m;j++{
            if  grid[i][j] == ‘1‘{
                bfs(grid,pair{i,j},n,m)
                res++
            }
        }
    }
    return res
}
type pair struct {
    x int
    y int
}
//注意一 不是else逻辑。
func bfs(grid [][]byte,p pair, n,m int) {
    if  grid[p.x][p.y] == ‘1‘{
        grid[p.x][p.y] = ‘0‘
        var queue []pair
        if p.x-1 >=0{
            queue = append(queue,pair{p.x-1,p.y})
        }
        if p.x+1 < n{
            queue = append(queue,pair{p.x+1 ,p.y})
        }
        if p.y-1>=0{
            queue = append(queue,pair{p.x,p.y-1})
        }
        if p.y+1<m{
            queue = append(queue,pair{p.x,p.y+1})
        }
        for len(queue) !=0 {
            bfs(grid,queue[0],n,m)
            queue = queue[1:]
        }
    }
    return 
}

func numIslands(grid [][]byte) int {
    n := len(grid)
    if n == 0{
        return 0
    }
    m := len(grid[0])
    res := 0
    for i:=0;i<n;i++{
        for j:=0;j<m;j++{
            if  grid[i][j] == ‘1‘{
                res++
                var queue []pair
                queue = append(queue,pair{i,j})
                for len(queue) !=0 {
                    p := queue[0]
                    queue = queue[1:]
                    if p.x-1 >=0 && grid[p.x-1][p.y] == ‘1‘{
                        queue = append(queue,pair{p.x-1,p.y})
                        grid[p.x-1][p.y] = ‘0‘
                    }
                    if p.x+1 < n && grid[p.x+1][p.y] == ‘1‘{
                        queue = append(queue,pair{p.x+1,p.y})
                        grid[p.x+1][p.y] = ‘0‘
                    }
                    if p.y-1 >=0 && grid[p.x][p.y-1] == ‘1‘{
                        queue = append(queue,pair{p.x,p.y-1})
                        grid[p.x][p.y-1] = ‘0‘
                    }
                    if p.y+1 < m && grid[p.x][p.y+1] == ‘1‘{
                        queue = append(queue,pair{p.x,p.y+1})
                        grid[p.x][p.y+1] = ‘0‘
                    }
                }
            }
        }
    }
    return res
}
type pair struct {
    x int
    y int
}