LeetCode - Number of Islands

Number of Islands

// BFS ---> note: this my cause issue when you encode the coordinates
public int numIslands(char[][] grid) {
        if(grid==null || grid.length==0) return 0;
        int count = 0;
        for(int i=0; i<grid.length; i++){
            for(int j=0; j<grid[0].length; j++){
                if(grid[i][j] == '1'){
                    count++;
                    setZeros(grid, i, j);
                }
            }
        }
        return count;
    }
    
    public void setZeros(char[][] grid, int x, int y){
        grid[x][y] = '0';
        Queue<Integer> queue = new LinkedList<Integer>();
        queue.offer(x*grid[0].length + y);
        while(!queue.isEmpty()){
            int cor = queue.poll();
            int row = cor / grid[0].length;
            int col = cor % grid[0].length;
            grid[row][col] = '0';
            if(row-1 >= 0 && grid[row-1][col] == '1'){
                queue.offer((row-1) * grid[0].length + col);
                grid[row-1][col] = '0';
            }
            if(row+1 < grid.length && grid[row+1][col] == '1'){
                queue.offer((row+1) * grid[0].length + col);
                grid[row+1][col] = '0';
            }
            if(col-1 >= 0 && grid[row][col-1] == '1'){
                queue.offer(row * grid[0].length + col-1);
                grid[row][col-1] = '0';
            }
            if(col+1 < grid[0].length && grid[row][col+1] == '1'){
                queue.offer(row * grid[0].length + col+1);
                grid[row][col+1] = '0';
            }
        }
    }

// DFS
public int numIslands(char[][] grid) {
        int ret = 0;
        if(grid == null || grid.length == 0 || grid[0].length == 0) return ret;
        for(int i=0; i<grid.length; i++){
            for(int j=0; j<grid[0].length; j++){
                if(grid[i][j] == '1'){
                    ret++;
                    helper(i,j, grid);
                }
            }
        }
        return ret;
    }
    
    public void helper(int x, int y, char[][] grid){
        if(x<0 || y<0 || x>=grid.length || y>=grid[0].length) return;
        if(grid[x][y] == '1'){
            grid[x][y] = '0';
            helper(x-1, y, grid);
            helper(x, y-1, grid);
            helper(x+1, y, grid);
            helper(x, y+1, grid);
        }
    }