_463.java

package com.fishercoder.solutions;
/**
 * 463. Island Perimeter
 *
 * You are given a map in form of a two-dimensional integer grid where 1 represents land and 0 represents water.
 * Grid cells are connected horizontally/vertically (not diagonally).
 * The grid is completely surrounded by water, and there is exactly one island (i.e., one or more connected land cells).
 * The island doesn't have "lakes" (water inside that isn't connected to the water around the island).
 * One cell is a square with side length 1.
 * The grid is rectangular, width and height don't exceed 100. Determine the perimeter of the island.

 Example:

 [[0,1,0,0],
 [1,1,1,0],
 [0,1,0,0],
 [1,1,0,0]]

 Answer: 16
 Explanation: The perimeter is the 16 yellow stripes in the image below:
 */
public class _463 {

    public static class Solution1 {
        /**
         * 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;
        }
    }
}