LeetCode: Number of Islands

// Given a 2d grid map of '1's (land) and '0's (water), count 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:

// 11110
// 11010
// 11000
// 00000
// Answer: 1

// Example 2:

// 11000
// 11000
// 00100
// 00011
// Answer: 3

public class NumberOfIslands {
    char[][] gridCopy;
 
    public int numIslands(char[][] grid) {
        //set grid copy to the current grid
        gridCopy = grid;
     
        //initialize number of islands to zero
        int numberOfIslands = 0;
     
        //iterate through every index of the grid
        for(int i = 0; i < grid.length; i++) {
            for(int j = 0; j < grid[0].length; j++) {
                //attempt to "sink" the current index of the grid
                numberOfIslands += sink(gridCopy, i, j);
             
            }
        }
     
        //return the total number of islands
        return numberOfIslands;
    }
 
    int sink(char[][] grid, int i, int j) {
        //check the bounds of i and j and if the current index is an island or not (1 or 0)
        if(i < 0 || i >= grid.length || j < 0 || j >= grid[0].length || grid[i][j] == '0') {
            return 0;
        }
     
        //set current index to 0
        grid[i][j] = '0';
     
        // sink all neighbors of current index
        sink(grid, i + 1, j);
        sink(grid, i - 1, j);
        sink(grid, i, j + 1);
        sink(grid, i, j - 1);
     
        //increment number of islands
        return 1;
    }
}