Add function Grid.subGridAt()

* It provides a view of a portion of the Grid.
* Use the SimpleCharGrid class instead of the
  simpleCharGridOf() function which was redundant.

Author: rhaendel

src/main/kotlin/de/ronny_h/aoc/extensions/grids/Grid.kt

@@ -81,6 +81,20 @@ abstract class Grid<T>(
         grid[position.row][position.col] = element
     }
 
+    /**
+     * @return a view of the portion of this Grid between the specified [row], [col] (inclusive) and [row] + [height], [col] + [width] (exclusive).
+     * The returned list of lists is backed by this Grid, so non-structural changes in the returned list are reflected
+     * in this Grid, and vice-versa.
+     * Structural changes in the base Grid make the behavior of the view undefined.
+     */
+    fun subGridAt(row: Int, col: Int, height: Int, width: Int = height): List<List<T>> {
+        return buildList {
+            for (r in row..<row + height) {
+                add(grid[r].subList(col, col + width))
+            }
+        }
+    }
+
     fun <R> forEachIndex(action: (row: Int, col: Int) -> R): Sequence<R> = sequence {
         for (row in grid.indices) {
             for (col in grid[0].indices) {

src/test/kotlin/de/ronny_h/aoc/extensions/grids/GridTest.kt

@@ -1,6 +1,7 @@
 package de.ronny_h.aoc.extensions.grids
 
 import com.github.stefanbirkner.systemlambda.SystemLambda.tapSystemOut
+import de.ronny_h.aoc.extensions.asList
 import io.kotest.assertions.throwables.shouldThrow
 import io.kotest.core.spec.style.StringSpec
 import io.kotest.data.forAll
@@ -10,15 +11,11 @@ import io.kotest.matchers.shouldNotBe
 
 class GridTest : StringSpec() {
 
-    private fun simpleCharGridOf(input: List<String>) = object : Grid<Char>(input, ' ') {
-        override fun Char.toElementType() = this
-    }
-
     private val newLine: String = System.lineSeparator()
 
     init {
         "a grid can be constructed from List of String" {
-            val grid = simpleCharGridOf(listOf("12", "34"))
+            val grid = SimpleCharGrid(listOf("12", "34"))
             grid shouldNotBe null
         }
 
@@ -33,13 +30,13 @@ class GridTest : StringSpec() {
         }
 
         "width and height have the right values" {
-            val grid = simpleCharGridOf(listOf("00", "00", "00"))
+            val grid = SimpleCharGrid(listOf("00", "00", "00"))
             grid.height shouldBe 3
             grid.width shouldBe 2
         }
 
         "charAt returns the input values from the right indices" {
-            val grid = simpleCharGridOf(listOf("12", "34"))
+            val grid = SimpleCharGrid(listOf("12", "34"))
             grid[0, 0] shouldBe '1'
             grid[0, 1] shouldBe '2'
             grid[1, 0] shouldBe '3'
@@ -57,15 +54,15 @@ class GridTest : StringSpec() {
         }
 
         "charAt with indices returns the same as charAt with Coordinates" {
-            val grid = simpleCharGridOf(listOf("12", "34"))
+            val grid = SimpleCharGrid(listOf("12", "34"))
             grid[0, 0] shouldBe grid.getAt(Coordinates(0, 0))
             grid[0, 1] shouldBe grid.getAt(Coordinates(0, 1))
             grid[1, 0] shouldBe grid.getAt(Coordinates(1, 0))
             grid[1, 1] shouldBe grid.getAt(Coordinates(1, 1))
         }
 
         "charAt with index out of the input values returns the nullElement of a Char Grid" {
-            val grid = simpleCharGridOf(listOf("12", "34"))
+            val grid = SimpleCharGrid(listOf("12", "34"), ' ')
             grid[-1, 0] shouldBe ' '
             grid[0, 2] shouldBe ' '
             grid[1, -1] shouldBe ' '
@@ -83,24 +80,37 @@ class GridTest : StringSpec() {
         }
 
         "setAt sets the element at the given coordinates" {
-            val grid = simpleCharGridOf(listOf("12", "34"))
+            val grid = SimpleCharGrid(listOf("12", "34"))
             grid.setAt(Coordinates(1, 0), '5')
             grid[0, 0] shouldBe '1'
             grid[0, 1] shouldBe '2'
             grid[1, 0] shouldBe '5'
             grid[1, 1] shouldBe '4'
         }
 
+        "subGridAt returns a sub grid at the given coordinates" {
+            val input = """
+                1234
+                5678
+                90AB
+                CDEF
+            """.asList()
+            SimpleCharGrid(input).subGridAt(1, 1, 2) shouldBe listOf(
+                listOf('6', '7'),
+                listOf('0', 'A'),
+            )
+        }
+
         "forEachIndex calls the provided function on each element in the expected order" {
-            val grid = simpleCharGridOf(listOf("12", "34"))
+            val grid = SimpleCharGrid(listOf("12", "34"))
             val chars = grid.forEachIndex { row, column ->
                 grid[row, column]
             }.toList()
             chars shouldBe listOf('1', '2', '3', '4')
         }
 
         "forEachElement calls the provided function on each element in the expected order" {
-            val grid = simpleCharGridOf(listOf("12", "34"))
+            val grid = SimpleCharGrid(listOf("12", "34"))
             val strings = grid.forEachElement { row, column, char ->
                 "$row,$column:$char"
             }.toList()
@@ -114,7 +124,7 @@ class GridTest : StringSpec() {
         }
 
         "find() finds all Coordinates" {
-            val grid = simpleCharGridOf(listOf("12", "34"))
+            val grid = SimpleCharGrid(listOf("12", "34"))
             forAll(
                 row('1', Coordinates(0, 0)),
                 row('2', Coordinates(0, 1)),
@@ -127,21 +137,21 @@ class GridTest : StringSpec() {
 
         "find() throws a NoSuchElementException if the value cannot be found" {
             shouldThrow<NoSuchElementException> {
-                simpleCharGridOf(listOf("12", "34")).find('5')
+                SimpleCharGrid(listOf("12", "34")).find('5')
             }
         }
 
         "printGrid prints the grid" {
             val output = tapSystemOut {
-                val grid = simpleCharGridOf(listOf("12", "34"))
+                val grid = SimpleCharGrid(listOf("12", "34"))
                 grid.printGrid()
             }
             output shouldBe "12${newLine}34$newLine"
         }
 
         "printGrid overrides specified coordinates" {
             val output = tapSystemOut {
-                val grid = simpleCharGridOf(listOf("12", "34"))
+                val grid = SimpleCharGrid(listOf("12", "34"))
                 grid.printGrid(
                     setOf(Coordinates(0, 1), Coordinates(1, 0))
                 )
@@ -151,7 +161,7 @@ class GridTest : StringSpec() {
 
         "printGrid overrides specified coordinates with given overrideChar" {
             val output = tapSystemOut {
-                val grid = simpleCharGridOf(listOf("12", "34"))
+                val grid = SimpleCharGrid(listOf("12", "34"))
                 grid.printGrid(
                     setOf(Coordinates(0, 1), Coordinates(1, 0)),
                     '?'
@@ -162,7 +172,7 @@ class GridTest : StringSpec() {
 
         "printGrid highlights specified coordinates with given highlightDirection's Char" {
             val output = tapSystemOut {
-                val grid = simpleCharGridOf(listOf("12", "34"))
+                val grid = SimpleCharGrid(listOf("12", "34"))
                 grid.printGrid(
                     highlightPosition = Coordinates(0, 1),
                     highlightDirection = Direction.SOUTH
@@ -173,7 +183,7 @@ class GridTest : StringSpec() {
 
         "printGrid - highlight has higher priority than overrides" {
             val output = tapSystemOut {
-                val grid = simpleCharGridOf(listOf("12", "34"))
+                val grid = SimpleCharGrid(listOf("12", "34"))
                 grid.printGrid(
                     overrides = setOf(Coordinates(0, 1)),
                     highlightPosition = Coordinates(0, 1),
@@ -185,7 +195,7 @@ class GridTest : StringSpec() {
 
         "printGrid - highlight without a direction falls back to overrides" {
             val output = tapSystemOut {
-                val grid = simpleCharGridOf(listOf("12", "34"))
+                val grid = SimpleCharGrid(listOf("12", "34"))
                 grid.printGrid(
                     overrides = setOf(Coordinates(0, 1)),
                     highlightPosition = Coordinates(0, 1),
@@ -195,12 +205,12 @@ class GridTest : StringSpec() {
         }
 
         "toString returns a string representation without any overrides" {
-            val grid = simpleCharGridOf(listOf("12", "34"))
+            val grid = SimpleCharGrid(listOf("12", "34"))
             grid.toString() shouldBe "12${newLine}34"
         }
 
         "toString with overrides returns a string representation with the given overrides" {
-            val grid = simpleCharGridOf(listOf("12", "34"))
+            val grid = SimpleCharGrid(listOf("12", "34"))
             grid.toString(setOf(Coordinates(1, 1)), 'o') shouldBe "12${newLine}3o"
         }
     }