463. Island Perimeter

package LeetCode_463

/**
 * 463. Island Perimeter
 * https://leetcode.com/problems/island-perimeter/description/
 *
 * You are given row x col grid representing a map where grid[i][j] = 1 represents land and grid[i][j] = 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", meaning the water inside 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.
 * */
class Solution {
    /*
    * solution: two loops, calculate total perimeter than minus total neighbours,
    * Time complexity:O(n), Space complexity:O(1)
    * */
    fun islandPerimeter(grid: Array<IntArray>): Int {
        if (grid.isEmpty()) {
            return 0
        }
        var area = 0
        var connect = 0
        val m = grid.size
        val n = grid[0].size
        for (i in 0 until m) {
            for (j in 0 until n) {
                if (grid[i][j] == 0) {
                    continue
                }
                area++
                //check 4 directions if a neighbours
                if (i > 0 && grid[i - 1][j] == 1) {
                    connect++
                }
                if (i < m - 1 && grid[i + 1][j] == 1) {
                    connect++
                }
                if (j > 0 && grid[i][j - 1] == 1) {
                    connect++
                }
                if (j < n - 1 && grid[i][j + 1] == 1) {
                    connect++
                }
            }
        }
        return area * 4 - connect
    }
}