From 771d4adb80fb27dd6ee633af9c4ad3887a74922e Mon Sep 17 00:00:00 2001
From: Jake Charman <jake@jakecharman.co.uk>
Date: Mon, 8 Dec 2025 15:05:15 +0000
Subject: [PATCH] 2025 Day 4

---
 2025/Day-04/day04.go | 101 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 101 insertions(+)
 create mode 100644 2025/Day-04/day04.go

diff --git a/2025/Day-04/day04.go b/2025/Day-04/day04.go
new file mode 100644
index 0000000..52da36e
--- /dev/null
+++ b/2025/Day-04/day04.go
@@ -0,0 +1,101 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"strings"
+)
+
+func readFile(f string) [][]string {
+	file, err := os.ReadFile(f)
+	if err != nil {
+		panic(err)
+	}
+	ret := [][]string{}
+	for _, line := range strings.Split(string(file), "\n") {
+		ret = append(ret, strings.Split(line, ""))
+	}
+	return ret
+}
+
+
+func lookAround(l [][]string, y int, x int) int {
+	yToCheck := []int{(y-1), y, (y+1)}
+	xToCheck := []int{(x-1), x, (x+1)}
+	numNearby := 0
+	for _, curY := range yToCheck {
+		if curY < 0 || curY > (len(l)-1) {
+			continue
+		}
+		for _, curX := range xToCheck {
+			if curX < 0 || curX > (len(l[curY])-1) {
+				continue
+			}
+			if curX == x && curY == y {
+				continue
+			}
+			if l[curY][curX] == "@" {
+				numNearby++
+			}
+		}
+	}
+	return numNearby
+}
+
+func removeRolls (l [][]string, toRemove [][]int) [][]string {
+	for _, r := range toRemove {
+		l[r[0]][r[1]] = "x"
+	}
+	return l
+}
+
+func runForklift (l [][]string) (int,[][]string) {
+	rollsToRemove := [][]int{}
+	numReachable := 0
+	for y := range l {
+		for x := range l[y] {
+			if l[y][x] != "@"{
+				continue
+			} else if lookAround(l, y, x) < 4 {
+				numReachable++
+				rollsToRemove = append(rollsToRemove, []int{y,x})
+			}
+		}
+	}
+	return numReachable, removeRolls(l, rollsToRemove)
+}
+
+func partOne() (int) {
+	input := readFile("input.txt")
+	numReachable := 0
+	for y := range input {
+		for x := range input[y] {
+			if input[y][x] == "."{
+				continue
+			} else if lookAround(input, y, x) < 4 {
+				numReachable++
+			}
+		}
+	}
+	return numReachable
+}
+
+func partTwo() int {
+	input := readFile("input.txt")
+	num := 0
+	numReachable := -1
+	for numReachable != 0 {
+		if numReachable != -1 {
+			num += numReachable
+		}
+		numReachable = 0
+		numReachable, input = runForklift(input)
+	}
+	num += numReachable
+	return num
+}
+
+func main() {
+	fmt.Println(partOne())
+	fmt.Println(partTwo())
+}