day13

2 files changed, 128 insertions, 0 deletions

diff --git a/day13/example.txt b/day13/example.txt
new file mode 100644
index 0000000..3b6b5cc
--- /dev/null
+++ b/day13/example.txt
@@ -0,0 +1,15 @@
+#.##..##.
+..#.##.#.
+##......#
+##......#
+..#.##.#.
+..##..##.
+#.#.##.#.
+
+#...##..#
+#....#..#
+..##..###
+#####.##.
+#####.##.
+..##..###
+#....#..#
diff --git a/day13/solution.zig b/day13/solution.zig
new file mode 100644
index 0000000..e3139fc
--- /dev/null
+++ b/day13/solution.zig
@@ -0,0 +1,113 @@
+const std = @import("std");
+const print = std.debug.print;
+const assert = std.debug.assert;
+const ArrayList = std.ArrayList;
+const HashMap = std.HashMap;
+const mem = std.mem;
+
+const fin = mem.trim(u8, @embedFile("./input.txt"), &std.ascii.whitespace);
+var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+const allocator = gpa.allocator();
+
+const Map = []const []const u8;
+
+fn cnt_diff(lhs: []const u8, rhs: []const u8) i64 {
+    var cnt: i64 = 0;
+
+    for (lhs, rhs) |l, b| {
+        if (l != b) {
+            cnt += 1;
+        }
+    }
+
+    return cnt;
+}
+
+fn check_eql(map: Map, i_: usize, j_: usize, tolerance_: i64) bool {
+    var i = i_;
+    var j = j_;
+    var tolerance = tolerance_;
+
+    while (i >= 0 and j < map.len) : ({
+        i = if (i > 0) i - 1 else break;
+        j += 1;
+    }) {
+        tolerance -= cnt_diff(map[i], map[j]);
+        if (tolerance < 0) {
+            return false;
+        }
+    }
+
+    return tolerance == 0;
+}
+
+fn transpose(map: Map) Map {
+    var transposed = allocator.alloc([]u8, map[0].len) catch unreachable;
+
+    for (transposed) |*trow| {
+        trow.* = allocator.alloc(u8, map.len) catch unreachable;
+    }
+
+    for (map, 0..) |row, i| {
+        for (row, 0..) |c, j| {
+            transposed[j][i] = c;
+        }
+    }
+
+    return transposed;
+}
+
+fn evaluate(map: Map, tolerance: i64) u64 {
+    const h = map.len;
+    const w = map[0].len;
+
+    // per row
+    for (0..h - 1, 1..) |i, j| {
+        if (check_eql(map, i, j, tolerance)) {
+            return 100 * j;
+        }
+    }
+
+    // per column
+    const transposed = transpose(map);
+    for (0..w - 1, 1..) |i, j| {
+        if (check_eql(transposed, i, j, tolerance)) {
+            return j;
+        }
+    }
+
+    unreachable;
+}
+
+pub fn solve(maps: []const Map) void {
+    var part1: u64 = 0;
+
+    for (maps) |map| {
+        part1 += evaluate(map, 0);
+    }
+    print("{d}\n", .{part1});
+
+    var part2: u64 = 0;
+
+    for (maps) |map| {
+        part2 += evaluate(map, 1);
+    }
+
+    print("{d}\n", .{part2});
+}
+
+pub fn main() !void {
+    var splitMirros = mem.splitSequence(u8, fin, "\n\n");
+    var maps = ArrayList([]const []const u8).init(allocator);
+
+    while (splitMirros.next()) |mirror| {
+        var splitLines = mem.splitScalar(u8, mirror, '\n');
+
+        var map = ArrayList([]const u8).init(allocator);
+        while (splitLines.next()) |line| {
+            try map.append(line);
+        }
+        try maps.append(map.items);
+    }
+    solve(maps.items);
+}