Island Perimeter

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.

Source

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
}

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Updated on 2021-10-23