island_perimeter

class Solution {

    int perimeterSum = 0;
    public int islandPerimeter(int[][] grid) {
        for(int i = 0; i < grid.length; i++){
            int[] row = grid[i];
            for(int j = 0; j < row.length; j++){
                if(grid[i][j] == 1){
                    perimeterSum += checkPerimeter( i, j , grid);
                }
            }
        }
        return perimeterSum;
    }

    private int checkPerimeter(int row, int col, int[][] grid){
        //if go out of boundaries or see a water
        if( row < 0 ||  col < 0 || grid.length <= row || grid[row].length <= col || grid[row][col] == 0 ){
            return 1;
        }

        if(grid[row][col] == -1){
            return 0;
        }

        grid[row][col] = -1; //visited

        int sum = 0;
        int[] x_move = new int[]{0, 1, 0 , -1};
        int[] y_move = new int[]{1, 0, -1, 0};

        for(int i = 0; i<4; i++){
            sum += checkPerimeter(row + x_move[i], col + y_move[i], grid);
        }
        // sum += checkPerimeter(row + 1, col, grid); // right
        // sum += checkPerimeter(row - 1, col, grid); // left
        // sum += checkPerimeter(row,     col - 1, grid); //up
        // sum += checkPerimeter(row,     col + 1, grid); //down
        return sum;
    }
}