day02: solve

src/day02.zig

@@ -0,0 +1,94 @@
+const std = @import("std");
+
+pub fn main() !void {
+    const input = @embedFile("data/day02.txt");
+    const target = Game{ .red = 12, .green = 13, .blue = 14 };
+    const sln = try solve(input, target);
+
+    std.debug.print("{d}\n", .{sln.possible});
+    std.debug.print("{d}\n", .{sln.powers});
+}
+
+const Day02Error = error{
+    MissingColon,
+};
+
+const Game = struct {
+    red: u32 = 0,
+    blue: u32 = 0,
+    green: u32 = 0,
+
+    fn parse(line: []const u8) !@This() {
+        var self = @This(){};
+        var n: u32 = 0;
+
+        const colon = std.mem.indexOfScalar(u8, line, ':') orelse return Day02Error.MissingColon;
+        var it = std.mem.splitAny(u8, line[colon + 1 ..], ",; ");
+        while (it.next()) |item| {
+            if (item.len == 0) {
+                continue;
+            }
+
+            switch (item[0]) {
+                'r' => self.red = @max(self.red, n),
+                'g' => self.green = @max(self.green, n),
+                'b' => self.blue = @max(self.blue, n),
+                '0'...'9' => n = try std.fmt.parseInt(u8, item, 10),
+                else => unreachable,
+            }
+        }
+
+        return self;
+    }
+
+    fn possible(self: @This(), other: @This()) bool {
+        return self.red <= other.red and self.green <= other.green and self.blue <= other.blue;
+    }
+};
+
+const Solution = struct {
+    possible: u32,
+    powers: u32,
+};
+
+fn solve(input: []const u8, target: Game) !Solution {
+    var possible: u32 = 0;
+    var powers: u32 = 0;
+
+    var index: u32 = 1;
+    var line_it = std.mem.splitScalar(u8, input, '\n');
+    while (line_it.next()) |line| : (index += 1) {
+        if (line.len == 0) {
+            continue;
+        }
+
+        const game = try Game.parse(line);
+        if (game.possible(target)) {
+            possible += index;
+        }
+        powers += game.red * game.blue * game.green;
+    }
+
+    return Solution{ .possible = possible, .powers = powers };
+}
+
+fn solveSample() !Solution {
+    const input =
+        \\Game 1: 3 blue, 4 red; 1 red, 2 green, 6 blue; 2 green
+        \\Game 2: 1 blue, 2 green; 3 green, 4 blue, 1 red; 1 green, 1 blue
+        \\Game 3: 8 green, 6 blue, 20 red; 5 blue, 4 red, 13 green; 5 green, 1 red
+        \\Game 4: 1 green, 3 red, 6 blue; 3 green, 6 red; 3 green, 15 blue, 14 red
+        \\Game 5: 6 red, 1 blue, 3 green; 2 blue, 1 red, 2 green
+    ;
+    return solve(input, .{ .red = 12, .blue = 14, .green = 13 });
+}
+
+test "silver" {
+    const sln = try solveSample();
+    try std.testing.expectEqual(@as(u32, 8), sln.possible);
+}
+
+test "gold" {
+    const sln = try solveSample();
+    try std.testing.expectEqual(@as(u32, 2286), sln.powers);
+}