200. Number of Islands

number-of-islands.go

// https://leetcode.com/problems/number-of-islands/
//
// Time: O(n*m)
// Space: O(n*m)
//
// n = number of rows, m = number of columns

// .................... //

func numIslands(grid [][]byte) int {
    n, m := len(grid), len(grid[0])

    var dfs func(i, j int)
    dfs = func(i, j int) {
        if i < 0 || i >= n || j < 0 || j >= m || grid[i][j] != '1' {
            return
        }

        grid[i][j] = '0'

        dfs(i+1, j)
        dfs(i, j+1)
        dfs(i-1, j)
        dfs(i, j-1)
    }

    res := 0

    for i := range n {
        for j := range m {
            if grid[i][j] == '1' {
                dfs(i, j)
                res++
            }
        }
    }

    return res
}