IslandPerimeter.java

// Solution 1
class Solution {

    public int islandPerimeter(int[][] grid) {
        int m = grid.length;
        int n = grid[0].length;
        boolean[][] visited = new boolean[m][n];
        for(int i=0;i<m;i++){
            for(int j=0;j<n;j++){
                if(grid[i][j] == 1){
                    return dfs(grid, i, j, visited);
                }
            }
        }
        return 0;
    }



    private int  dfs(int[][] grid, int i, int j, boolean[][] visited){
        if(i<0 || j<0 || i>=grid.length || j>=grid[0].length || grid[i][j] == 0){
            return 1;
        }
        if(visited[i][j]){
            return 0;
        }
        visited[i][j] = true;
        return dfs(grid, i-1,j, visited) + dfs(grid, i+1,j, visited) + dfs(grid, i,j-1, visited) + dfs(grid, i,j+1, visited);

    }
}

// Solution 2
class Solution {

    // At every point count the no of surrounding zeros
    public int islandPerimeter(int[][] grid) {
        int m = grid.length;
        if(m<=0){
            return 0;
        }
        int n= grid[0].length;
        if(n<=0){
            return 0;
        }

        int count =0;
        for(int i=0;i<m;i++){

            for(int j=0;j<n;j++) {
                if(grid[i][j]==1){
                    if(i==0 || grid[i-1][j]==0) count++;

                    if(j==0 || grid[i][j-1]==0) count++;

                    if(i+1==m || grid[i+1][j]==0) count++;

                    if(j+1==n || grid[i][j+1]==0) count++;
                }
            }


        }
        return count;
    }
}