From 151dc8653420506e7d81b4728de3aae6a9633e42 Mon Sep 17 00:00:00 2001
From: andrewlalis <andrewlalisofficial@gmail.com>
Date: Sun, 3 Dec 2023 09:36:41 -0500
Subject: [PATCH] Added day 3 solution.

---
 day_3/input.txt  | 140 +++++++++++++++++++++++++++++++++++++++++++++++
 day_3/sample.txt |  10 ++++
 day_3/solution.d |  85 ++++++++++++++++++++++++++++
 3 files changed, 235 insertions(+)
 create mode 100644 day_3/input.txt
 create mode 100644 day_3/sample.txt
 create mode 100644 day_3/solution.d

diff --git a/day_3/input.txt b/day_3/input.txt
new file mode 100644
index 0000000..2fdc084
--- /dev/null
+++ b/day_3/input.txt
@@ -0,0 +1,140 @@
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+...491.842.....948*..................338.....*......=...........-...309.......633*....*....................*990...706...452......*..+.......
+...*...*....................426........*..408.........................*............659...............250.........&.......*.....767...403....
+363.....961...959#.508*223......843.406..........690................%..479.....................398.../....*............458..................
+......=.........................................*....@946........767.........907=.................@....158.850..+670..............10*790....
+.......39.306...679.%113...............665....874....................597...................861.........................840...855............
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diff --git a/day_3/sample.txt b/day_3/sample.txt
new file mode 100644
index 0000000..624ea4f
--- /dev/null
+++ b/day_3/sample.txt
@@ -0,0 +1,10 @@
+467..114..
+...*......
+..35..633.
+......#...
+617*......
+.....+.58.
+..592.....
+......755.
+...$.*....
+.664.598..
\ No newline at end of file
diff --git a/day_3/solution.d b/day_3/solution.d
new file mode 100644
index 0000000..74d7013
--- /dev/null
+++ b/day_3/solution.d
@@ -0,0 +1,85 @@
+import std.stdio;
+import std.file;
+import std.string;
+import std.algorithm;
+import std.array;
+import std.ascii : isDigit;
+import std.conv;
+
+struct Point {const int x, y;}
+
+char getChar(ref char[][] array, int x, int y) {
+    if (y >= 0 && y < array.length && x >= 0 && x < array[y].length) return array[y][x];
+    return '.';
+}
+
+void part1() {
+    char[][] schematic = File("input.txt").byLineCopy()
+        .map!(line => cast(char[])line)
+        .array();
+
+    bool hasAdjacentSymbol(int x, int y, int length) {
+        for (int i = y-1; i < y+2; i++) {
+            for (int j = x-1; j < x+length+1; j++) {
+                const char c = getChar(schematic, j, i);
+                if (c != '.' && !isDigit(c)) return true;
+            }
+        }
+        return false;
+    }
+
+    int sum = 0;
+    for (int y = 0; y < schematic.length; y++) {
+        for (int x = 0; x < schematic[y].length; x++) {
+            if (isDigit(schematic[y][x])) {
+                int length = 1;
+                while (x + length < schematic[y].length && isDigit(schematic[y][x+length])) length++;
+                if (hasAdjacentSymbol(x, y, length)) {
+                    int n = schematic[y][x..x+length].to!int;
+                    sum += n;
+                }
+                x += length;
+            }
+        }
+    }
+    writeln(sum);
+}
+
+void part2() {
+    char[][] schematic = File("input.txt").byLineCopy()
+        .map!(line => cast(char[])line)
+        .array();
+
+    Point[] findGears(int x, int y, int length) {
+        Point[] gears;
+        for (int i = y-1; i < y+2; i++) {
+            for (int j = x-1; j < x+length+1; j++) {
+                if (getChar(schematic, j, i) == '*') gears ~= Point(j, i);
+            }
+        }
+        return gears;
+    }
+
+    int[][Point] gearNumbers;
+    for (int y = 0; y < schematic.length; y++) {
+        for (int x = 0; x < schematic[y].length; x++) {
+            if (isDigit(schematic[y][x])) {
+                int length = 1;
+                while (x + length < schematic[y].length && isDigit(schematic[y][x+length])) length++;
+                int n = schematic[y][x..x+length].to!int;
+                Point[] gears = findGears(x, y, length);
+                foreach (Point gear; gears) {
+                    if (gear !in gearNumbers) gearNumbers[gear] = [];
+                    gearNumbers[gear] ~= n;
+                }
+                x += length;
+            }
+        }
+    }
+    gearNumbers.values.map!(a => a.length == 2 ? a[0] * a[1] : 0).sum.writeln();
+}
+
+void main() {
+    part1();
+    part2();
+}