Day 14.

src/Utils.kt

@@ -96,10 +96,8 @@ class CharGrid {
         height = inputGrid.size
     }
 
-    @Deprecated("Use RelPos version instead")
     operator fun get(col: Int, row: Int) = getOrNull(col, row) ?: bChar
 
-    @Deprecated("Use RelPos version instead")
     operator fun set(col: Int, row: Int, newChar: Char?) {
         if (newChar != null && isInside(col, row)) data[row][col] = newChar
     }

src/aoc2024/Day14.kt

@@ -0,0 +1,89 @@
+package aoc2024
+
+import CharGrid
+import println
+import readInput
+
+/*
+--- Day 14: Restroom Redoubt ---
+https://adventofcode.com/2024/day/14
+*/
+fun main() {
+
+    val inlineTestInput = """
+p=0,4 v=3,-3
+p=6,3 v=-1,-3
+p=10,3 v=-1,2
+p=2,0 v=2,-1
+p=0,0 v=1,3
+p=3,0 v=-2,-2
+p=7,6 v=-1,-3
+p=3,0 v=-1,-2
+p=9,3 v=2,3
+p=7,3 v=-1,2
+p=2,4 v=2,-3
+p=9,5 v=-3,-3
+"""
+
+    fun part1(input: List<String>, time: Int, w: Int, h: Int): Int {
+        val robots = input.map { "p=(\\d+),(\\d+) v=(-?\\d+),(-?\\d+)".toRegex().find(it)!!.groupValues.drop(1).map { it.toInt() }.toIntArray() }
+        for (r in robots) {
+            r[0] = (r[0] + time * (r[2] + w)) % w
+            r[1] = (r[1] + time * (r[3] + h)) % h
+        }
+        val q1 = robots.count { it[0] < w / 2 && it[1] < h / 2 }
+        val q2 = robots.count { it[0] > w / 2 && it[1] < h / 2 }
+        val q3 = robots.count { it[0] < w / 2 && it[1] > h / 2 }
+        val q4 = robots.count { it[0] > w / 2 && it[1] > h / 2 }
+        return q1 * q2 * q3 * q4
+    }
+
+    fun part2(input: List<String>, w: Int, h: Int): Int {
+        val robots = input.map { "p=(\\d+),(\\d+) v=(-?\\d+),(-?\\d+)".toRegex().find(it)!!.groupValues.drop(1).map { it.toInt() }.toIntArray() }
+        /*
+          either: 1) x == w/2 -+ c, y == c c in [0..w/2]
+          or    : 2) x == w/2, y in (w/2..h)
+
+          1) px + t * (vx + w) % w = w/2 - c; py + t * (vy + h) % h = c
+             px + t * (vx + w) % w = w/2 - (py + t * (vy + h) % h)
+             (px - py) + t * (((vx + w) % w) - ((vy + h) % h)) = w/2
+
+          2) px == w/2, py > w/2 % h
+         */
+        val z = Array(robots.size) { IntArray(4) }
+        for (t in 1..1000000000L) {
+            /*val good = robots.all {
+                val x = ((it[0] + t * (it[2] + w)) % w).toInt()
+                val y = ((it[1] + t * (it[3] + h)) % h).toInt()
+                (y <= w / 2 && ((x >= w / 2 - y) && (x <= w / 2 + y))) || (x == w / 2 && y > w / 2)
+            }
+            if (!good) continue*/
+            for ((i, r) in robots.withIndex()) {
+                z[i][0] = ((r[0] + t * (r[2] + w)) % w).toInt()
+                z[i][1] = ((r[1] + t * (r[3] + h)) % h).toInt()
+            }
+            if (z.map { it[0] to it[1] }.distinct().count() < robots.size) continue
+            println("Solution $t")
+            val grid = CharGrid(w, h, '.')
+            z.forEach { grid[it[0], it[1]] = '*' }
+            grid.debug()
+            println()
+            break
+        }
+        return 0
+    }
+
+    // test if implementation meets criteria from the description, like:
+    val testInput = inlineTestInput.trim().reader().readLines()
+    //val testInput = readInput("aoc2024/Day14_test")
+    val testInputPart1Result = part1(testInput, 100, 11, 7)
+    println("Part 1 Test: $testInputPart1Result")
+    //val testInputPart2Result = part2(testInput, 11, 7)
+    //println("Part 2 Test: $testInputPart2Result")
+    check(testInputPart1Result == 12)
+    //check(testInputPart2Result == 0)
+
+    val input = readInput("aoc2024/Day14")
+    part1(input, 100, 101, 103).println()
+    part2(input, 101, 103).println()
+}