[aoc/2021] Add day 8

Part two is the ziggiest Zig I've ever written!

2 files changed, 78 insertions, 0 deletions

diff --git a/aoc/2021/08/part-one.zig b/aoc/2021/08/part-one.zig
new file mode 100644
index 0000000..0a9ad93
--- /dev/null
+++ b/aoc/2021/08/part-one.zig
@@ -0,0 +1,18 @@
+const print = std.debug.print;
+const std = @import("std");
+const tokenize = std.mem.tokenize;
+
+pub fn main() !void {
+    var count: usize = 0;
+    defer print("{}\n", .{ count });
+
+    var input = tokenize(@embedFile("input"), "\n");
+    while (input.next()) |line| {
+        var output = tokenize(line[61..], " ");
+        while (output.next()) |digit|
+            switch (digit.len) {
+                2, 3, 4, 7 => count += 1,
+                else => {},
+            };
+    }
+}
diff --git a/aoc/2021/08/part-two.zig b/aoc/2021/08/part-two.zig
new file mode 100644
index 0000000..74db158
--- /dev/null
+++ b/aoc/2021/08/part-two.zig
@@ -0,0 +1,60 @@
+const indexOfScalar = std.mem.indexOfScalar;
+const print = std.debug.print;
+const std = @import("std");
+const tokenize = std.mem.tokenize;
+
+const digits = [_]u7{
+    0b1110111,
+    0b0010010,
+    0b1011101,
+    0b1011011,
+    0b0111010,
+    0b1101011,
+    0b1101111,
+    0b1010010,
+    0b1111111,
+    0b1111011,
+    //8687497
+};
+
+pub fn main() !void {
+    var sum: usize = 0;
+    defer print("{}\n", .{ sum });
+
+    var input = tokenize(@embedFile("input"), "\n");
+    while (input.next()) |line| {
+        var freq = [_]u8{ 0 } ** 7;
+        for (line[0..58]) |c|
+            switch (c) {
+                'a'...'g' => freq[c - 'a'] += 1,
+                else => {},
+            };
+
+        var patterns = tokenize(line[0..58], " ");
+        while (patterns.next()) |p|
+            if (p.len == 4)
+                for (freq) |*f, i| {
+                    if (indexOfScalar(u8, p, 'a' + @intCast(u8, i))) |_|
+                        f.* -= 6;
+                }; // 8687497 to 8021437
+
+        var display: [7]u3 = undefined;
+        for (freq) |f, i|
+            display[i] = switch (f) {
+                8 => 0, 0 => 1, 2 => 2, 1 => 3, 4 => 4, 3 => 5, 7 => 6,
+                else => unreachable,
+            };
+
+        var output = tokenize(line[61..], " ");
+        var pow: usize = 1000;
+        while (output.next()) |s| : (pow /= 10) {
+            var digit: u7 = 0;
+            for (s) |c|
+                digit |= @as(u7, 1) << display[c - 'a'];
+            sum += pow * for (digits) |d, i| {
+                if (@bitReverse(u7, d) == digit) // edian
+                    break i;
+            } else unreachable;
+        }
+    }
+}