day(25): add solution

Signed-off-by: Matej Focko <mfocko@redhat.com>

src/year2021/day25/Day25.kt

@@ -0,0 +1,65 @@
+package year2021.day25
+
+import product
+import readInput
+
+typealias Cucumbers = List<List<Char>>
+
+fun printCucumbers(input: Cucumbers) {
+    println(input.joinToString("\n") { it.joinToString("") })
+}
+
+fun isFreeLocation(input: Cucumbers, x: Int, y: Int): Boolean =
+    input[y][x] == '.'
+
+fun moveSomewhere(input: Cucumbers, facing: Char, dx: Int, dy: Int): Cucumbers {
+    val output = input.toList().map { it.toMutableList() }
+
+    val height = input.size
+    val width = input.first().size
+    for ((y, x) in product(input.indices, input.first().indices)) {
+        if (input[y][x] != facing) {
+            continue
+        }
+
+        val newX = (x + dx) % width
+        val newY = (y + dy) % height
+        if (isFreeLocation(input, newX, newY)) {
+            output[y][x] = '.'
+            output[newY][newX] = facing
+        }
+    }
+
+    return output
+}
+
+fun moveEast(input: Cucumbers): Cucumbers = moveSomewhere(input, '>', 1, 0)
+fun moveSouth(input: Cucumbers): Cucumbers = moveSomewhere(input, 'v', 0, 1)
+fun move(input: Cucumbers): Cucumbers = moveSouth(moveEast(input))
+
+fun part1(input: Cucumbers): Int {
+    var counter = 0
+    var previous: Cucumbers = emptyList()
+    var current = input
+
+    while (previous != current) {
+        previous = current
+        current = move(previous)
+        counter++
+    }
+
+    return counter
+}
+
+fun part2(input: Cucumbers): String = "Merry Christmas I guess…"
+
+fun main() {
+    val smallerSample = readInput(25, "smaller_sample").map(String::toList)
+    val sample = readInput(25, "sample").map(String::toList)
+    val input = readInput(25, "input").map(String::toList)
+
+    check(part1(sample) == 58)
+    println(part1(input))
+
+    println(part2(input))
+}

src/year2021/day25/sample.txt

@@ -0,0 +1,9 @@
+v...>>.vv>
+.vv>>.vv..
+>>.>v>...v
+>>v>>.>.v.
+v>v.vv.v..
+>.>>..v...
+.vv..>.>v.
+v.v..>>v.v
+....v..v.>

src/year2021/day25/smaller_sample.txt

@@ -0,0 +1,7 @@
+...>...
+.......
+......>
+v.....>
+......>
+.......
+..vvv..