Number of islands - Test code

gistfile1.txt

/**
 * Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water), return the number of islands.
 * An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. 
 * You may assume all four edges of the grid are all surrounded by water.
 *
 * Example 1:
 *
 * Input: grid = [
 *   ["1","1","1","1","0"],
 *   ["1","1","0","1","0"],
 *   ["1","1","0","0","0"],
 *   ["0","0","0","0","0"]
 * ]
 * Output: 1
 * Example 2:
 *
 * Input: grid = [
 *   ["1","1","0","0","0"],
 *   ["1","1","0","0","0"],
 *   ["0","0","1","0","0"],
 *   ["0","0","0","1","1"]
 * ]
 * Output: 3
 */
class Solution {
    public int numIslands(char[][] grid) {
        
        int m = grid.length;
        int n = grid[0].length;

        int islandsNumber = 0;

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

              if(grid[i][j] == '1') {
                processCell(i, j, grid, m, n); 
                islandsNumber++;
              }
            } 
        }

        return islandsNumber;
    }

    public void processCell(int x, int y, char[][] grid, int m, int n) {

        if(grid[x][y] == '0') {
            return;
        }

        grid[x][y] = '0';

        // check left
        if(y > 0) {
            processCell(x, y - 1, grid, m, n);
        }

        // check up
        if(x > 0) {
            processCell(x - 1, y, grid, m, n);
        }

        // check right
        if(y < n - 1) {
            processCell(x, y + 1, grid, m, n);
        }
        
        // check down
        if(x < m - 1) {
            processCell(x + 1, y, grid, m, n);
        }
    }
}