From 68f15009538bf5f96e5eb352ed1ce1d913dd9025 Mon Sep 17 00:00:00 2001
From: Dustin Swan <dustin@dustinswan.com>
Date: Wed, 13 Dec 2023 19:17:29 -0700
Subject: [PATCH] Day 13. still haven't finished day 12. Today was so easy
 compared to yesterday.

---
 day13/main.zig | 119 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 119 insertions(+)
 create mode 100644 day13/main.zig

diff --git a/day13/main.zig b/day13/main.zig
new file mode 100644
index 0000000..d67a28a
--- /dev/null
+++ b/day13/main.zig
@@ -0,0 +1,119 @@
+const std = @import("std");
+
+pub fn main() !void {
+    const content = @embedFile("data.txt");
+
+    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+    const allocator = gpa.allocator();
+
+    // yo dog
+    var grids = std.ArrayList(std.ArrayList(std.ArrayList(u8))).init(allocator);
+    var sections = std.mem.split(u8, content, "\n\n");
+
+    while (sections.next()) |section| {
+        var lines = std.mem.split(u8, section, "\n");
+        var gridArrayList = std.ArrayList(std.ArrayList(u8)).init(allocator);
+
+        while (lines.next()) |line| {
+            if (line.len < 1) {
+                break;
+            }
+
+            var lineArrayList = std.ArrayList(u8).init(allocator);
+            for (line) |char| {
+                try lineArrayList.append(char);
+            }
+            try gridArrayList.append(lineArrayList);
+        }
+
+        try grids.append(gridArrayList);
+    }
+
+    var part1: usize = 0;
+    var part2: usize = 0;
+
+    for (grids.items) |grid| {
+        const transposed = try transpose(grid, allocator);
+
+        const rowReflection = findRowReflection(grid);
+        const columnReflection = findRowReflection(transposed);
+
+        part1 += 100 * (rowReflection orelse 0) + (columnReflection orelse 0);
+
+        const rowSmudge = findSmudge(grid);
+        const colSmudge = findSmudge(transposed);
+
+        part2 += 100 * (rowSmudge orelse 0) + (colSmudge orelse 0);
+    }
+
+    std.debug.print("part1 {d}\n", .{part1});
+    std.debug.print("part2 {d}\n", .{part2});
+}
+
+fn findSmudge(grid: std.ArrayList(std.ArrayList(u8))) ?usize {
+    const height = grid.items.len;
+
+    for (1..height) |row| {
+        var numDiff: u8 = 0;
+
+        for (1..row + 1) |d| {
+            const row1 = grid.items[row - d];
+            const row2 = grid.items[row + d - 1];
+
+            for (0..row1.items.len) |i| {
+                if (row1.items[i] != row2.items[i]) {
+                    numDiff += 1;
+                }
+            }
+            if (numDiff > 1) {
+                break;
+            }
+
+            if (row - d == 0 or row + d == height) {
+                break;
+            }
+        }
+
+        if (numDiff == 1) {
+            return row;
+        }
+    }
+    return null;
+}
+
+fn findRowReflection(grid: std.ArrayList(std.ArrayList(u8))) ?usize {
+    const height = grid.items.len;
+
+    for (1..height) |row| {
+        for (1..row + 1) |d| {
+            const row1 = grid.items[row - d];
+            const row2 = grid.items[row + d - 1];
+            if (!std.mem.eql(u8, row1.items, row2.items)) {
+                break;
+            }
+
+            if (row - d == 0 or row + d == height) {
+                return row;
+            }
+        }
+    }
+    return null;
+}
+
+fn transpose(grid: std.ArrayList(std.ArrayList(u8)), allocator: std.mem.Allocator) !std.ArrayList(std.ArrayList(u8)) {
+    const height = grid.items.len;
+    const width = grid.items[0].items.len;
+
+    var grid2 = std.ArrayList(std.ArrayList(u8)).init(allocator);
+    for (0..width) |c| {
+        var row = std.ArrayList(u8).init(allocator);
+
+        for (0..height) |r| {
+            try row.append(grid.items[r].items[c]);
+        }
+
+        try grid2.append(row);
+    }
+
+    return grid2;
+}