IslandPerimeter.kt

package questions

import _utils.UseCommentAsDocumentation
import utils.shouldBe

/**
 * 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.
 *
 * <img src="https://assets.leetcode.com/uploads/2018/10/12/island.png" height="150" width="150"/>
 * Determine the perimeter of the island.
 *
 * [Source](https://leetcode.com/problems/island-perimeter/)
 */
@UseCommentAsDocumentation
private fun islandPerimeter(grid: Array<IntArray>): Int {
    var result = 0
    val colSize = grid[0].lastIndex
    for (row in 0..grid.lastIndex) {
        for (col in 0..colSize) {
            val current = grid[row][col]
            if (current == 0) {
                //  not a land
                continue
            }
            val left = grid[row].getOrNull(col - 1)
            val right = grid[row].getOrNull(col + 1)
            val top = grid.getOrNull(row - 1)?.getOrNull(col)
            val bottom = grid.getOrNull(row + 1)?.getOrNull(col)
            // check if there is land on each of its direction
            if (left == null || left == 0) result++
            if (right == null || right == 0) result++
            if (top == null || top == 0) result++
            if (bottom == null || bottom == 0) result++
        }
    }
    return result
}

fun main() {
    islandPerimeter(
        arrayOf(intArrayOf(0, 1, 0, 0), intArrayOf(1, 1, 1, 0), intArrayOf(0, 1, 0, 0), intArrayOf(1, 1, 0, 0))
    ) shouldBe 16
}