From 24669a60f06bde387fd2d16642f7585849dca060 Mon Sep 17 00:00:00 2001
From: xeals <dev@xeal.me>
Date: Wed, 6 Dec 2023 16:25:34 +1100
Subject: [PATCH] wtf happened in day06

---
 src/day06.zig | 85 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 85 insertions(+)
 create mode 100644 src/day06.zig

diff --git a/src/day06.zig b/src/day06.zig
new file mode 100644
index 0000000..e874dac
--- /dev/null
+++ b/src/day06.zig
@@ -0,0 +1,85 @@
+const std = @import("std");
+const util = @import("util.zig");
+const mem = std.mem;
+
+pub fn main() !void {
+    const input = @embedFile("data/day06.txt");
+    const sln = try solve(util.gpa, input);
+    std.debug.print("{d}\n", .{sln.a});
+    std.debug.print("{d}\n", .{sln.b});
+}
+
+const Solution = struct {
+    a: usize,
+    b: usize,
+};
+
+const Race = struct {
+    time: usize,
+    distance: usize,
+};
+
+fn solve(alloc: mem.Allocator, input: []const u8) !Solution {
+    const races: []Race = r: {
+        var it = util.splitLines(input);
+        const times = try util.parseIntsScalar(usize, alloc, it.next().?[10..], .{});
+        const distances = try util.parseIntsScalar(usize, alloc, it.next().?[10..], .{});
+        defer alloc.free(times);
+        defer alloc.free(distances);
+        var al = try std.ArrayList(Race).initCapacity(alloc, times.len);
+        for (times, distances) |t, d| {
+            try al.append(.{ .time = t, .distance = d });
+        }
+        break :r try al.toOwnedSlice();
+    };
+    defer alloc.free(races);
+
+    const bigRace: Race = r: {
+        var it = util.splitLines(input);
+        var vals: [2]usize = undefined;
+        for (0..vals.len) |i| {
+            const line = try mem.replaceOwned(u8, alloc, it.next().?[10..], " ", "");
+            defer alloc.free(line);
+            vals[i] = try std.fmt.parseInt(usize, line, 10);
+        }
+        break :r .{ .time = vals[0], .distance = vals[1] };
+    };
+
+    var result: usize = 1;
+    for (races) |race| {
+        var winning: usize = 0;
+        for (0..race.time - 1) |speed| {
+            const distance = speed * (race.time - speed);
+            if (distance > race.distance) winning += 1;
+        }
+        result *= winning;
+    }
+
+    var result2: usize = 1;
+    var winning2: usize = 0;
+    for (0..bigRace.time - 1) |speed| {
+        const distance = speed * (bigRace.time - speed);
+        if (distance > bigRace.distance) winning2 += 1;
+    }
+    result2 *= winning2;
+
+    return .{ .a = result, .b = result2 };
+}
+
+test "silver" {
+    const input =
+        \\Time:      7  15   30
+        \\Distance:  9  40  200
+    ;
+    const sln = try solve(std.testing.allocator, input);
+    try std.testing.expectEqual(@as(usize, 288), sln.a);
+}
+
+test "gold" {
+    const input =
+        \\Time:      7  15   30
+        \\Distance:  9  40  200
+    ;
+    const sln = try solve(std.testing.allocator, input);
+    try std.testing.expectEqual(@as(usize, 288), sln.b);
+}