diff --git a/src/aoc2024/Day04.kt b/src/aoc2024/Day04.kt
new file mode 100644
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+++ b/src/aoc2024/Day04.kt
@@ -0,0 +1,113 @@
+package aoc2024
+
+import CharGrid
+import RelPos
+import println
+import readInput
+
+/*
+--- Day 4: Ceres Search ---
+"Looks like the Chief's not here. Next!" One of The Historians pulls out a device and pushes the only button on it. After a brief flash, you recognize the interior of the Ceres monitoring station!
+As the search for the Chief continues, a small Elf who lives on the station tugs on your shirt; she'd like to know if you could help her with her word search (your puzzle input). She only has to find one word: XMAS.
+This word search allows words to be horizontal, vertical, diagonal, written backwards, or even overlapping other words. It's a little unusual, though, as you don't merely need to find one instance of XMAS - you need to find all of them. Here are a few ways XMAS might appear, where irrelevant characters have been replaced with .:
+..X...
+.SAMX.
+.A..A.
+XMAS.S
+.X....
+
+The actual word search will be full of letters instead. For example:
+MMMSXXMASM
+MSAMXMSMSA
+AMXSXMAAMM
+MSAMASMSMX
+XMASAMXAMM
+XXAMMXXAMA
+SMSMSASXSS
+SAXAMASAAA
+MAMMMXMMMM
+MXMXAXMASX
+
+In this word search, XMAS occurs a total of 18 times; here's the same word search again, but where letters not involved in any XMAS have been replaced with .:
+....XXMAS.
+.SAMXMS...
+...S..A...
+..A.A.MS.X
+XMASAMX.MM
+X.....XA.A
+S.S.S.S.SS
+.A.A.A.A.A
+..M.M.M.MM
+.X.X.XMASX
+
+Take a look at the little Elf's word search. How many times does XMAS appear?
+
+*/
+fun main() {
+
+    val inlineTestInput = """
+MMMSXXMASM
+MSAMXMSMSA
+AMXSXMAAMM
+MSAMASMSMX
+XMASAMXAMM
+XXAMMXXAMA
+SMSMSASXSS
+SAXAMASAAA
+MAMMMXMMMM
+MXMXAXMASX
+"""
+
+    fun part1(input: List<String>): Int {
+        val grid = CharGrid(input)
+        val relposes = listOf(
+            listOf(RelPos(0, 0), RelPos(1, 0), RelPos(2, 0), RelPos(3, 0)),
+            listOf(RelPos(0, 0), RelPos(-1, 0), RelPos(-2, 0), RelPos(-3, 0)),
+            listOf(RelPos(0, 0), RelPos(1, 1), RelPos(2, 2), RelPos(3, 3)),
+            listOf(RelPos(0, 0), RelPos(-1, -1), RelPos(-2, -2), RelPos(-3, -3)),
+            listOf(RelPos(0, 0), RelPos(-1, 1), RelPos(-2, 2), RelPos(-3, 3)),
+            listOf(RelPos(0, 0), RelPos(1, -1), RelPos(2, -2), RelPos(3, -3)),
+            listOf(RelPos(0, 0), RelPos(0, 1), RelPos(0, 2), RelPos(0, 3)),
+            listOf(RelPos(0, 0), RelPos(0, -1), RelPos(0, -2), RelPos(0, -3)),
+        )
+        var sum = 0
+        for (x in 0 until grid.width) {
+            for (y in 0 until grid.height) {
+                for (rp in relposes) {
+                    val st = grid.collectRelative(x, y, rp).joinToString("")
+                    if (st == "XMAS") sum++
+                }
+            }
+        }
+        return sum
+    }
+
+    fun part2(input: List<String>): Int {
+        val grid = CharGrid(input)
+        val rp1 = listOf(RelPos(-1, -1), RelPos(0, 0), RelPos(1, 1))
+        val rp2 = listOf(RelPos(-1, 1), RelPos(0, 0), RelPos(1, -1))
+        var sum = 0
+        for (x in 0 until grid.width) {
+            for (y in 0 until grid.height) {
+                val st1 = grid.collectRelative(x, y, rp1).joinToString("")
+                val st2 = grid.collectRelative(x, y, rp2).joinToString("")
+                if ((st1 == "MAS" || st1 == "SAM") && (st2 == "MAS" || st2 == "SAM")) sum++
+            }
+        }
+        return sum
+    }
+
+    // test if implementation meets criteria from the description, like:
+    val testInput = inlineTestInput.trim().reader().readLines()
+    //val testInput = readInput("aoc2024/Day04_test")
+    val testInputPart1Result = part1(testInput)
+    println("Part 1 Test: $testInputPart1Result")
+    val testInputPart2Result = part2(testInput)
+    println("Part 2 Test: $testInputPart2Result")
+    check(testInputPart1Result == 18)
+    check(testInputPart2Result == 9)
+
+    val input = readInput("aoc2024/Day04")
+    part1(input).println()
+    part2(input).println()
+}