IslandPerimeter.java

package easy;

public class IslandPerimeter {
    /**Inspired by this post: https://discuss.leetcode.com/topic/68983/java-9-line-solution-add-4-for-each-land-and-remove-2-for-each-internal-edge
     * 1. we increment the count by 4 whenever we encounter an island
     * 2. also, we check in two directions: island's left and island's top, we only check these two directions,
     * see if this island has any island neighbors, if so, we'll deduct two from it.*/
    public int islandPerimeter(int[][] grid) {
        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 += 4;
                    if(i > 0 && grid[i-1][j] == 1) count -= 2;
                    if(j > 0 && grid[i][j-1] == 1) count -= 2;
                }
            }
        }
        return count;
    }
}