From a76b193a8a2b661d4fe50dc0eb56bee4016ed778 Mon Sep 17 00:00:00 2001
From: John Costa <johncosta027@gmail.com>
Date: Wed, 6 Dec 2023 22:25:02 +0000
Subject: [PATCH] Day 6: Nice!

---
 AdventOfCode2023/src/day6/day6.zig | 133 +++++++++++++++++++++++++++++
 AdventOfCode2023/src/main.zig      |   7 +-
 2 files changed, 137 insertions(+), 3 deletions(-)
 create mode 100644 AdventOfCode2023/src/day6/day6.zig

diff --git a/AdventOfCode2023/src/day6/day6.zig b/AdventOfCode2023/src/day6/day6.zig
new file mode 100644
index 0000000..c3fb136
--- /dev/null
+++ b/AdventOfCode2023/src/day6/day6.zig
@@ -0,0 +1,133 @@
+const std = @import("std");
+const math = std.math;
+const print = std.debug.print;
+
+const QuadraticSolution = struct {
+    x1: f128,
+    x2: f128,
+};
+
+const Quadratic = struct {
+    a: i128,
+    b: i128,
+    c: i128,
+
+    pub fn solve(self: Quadratic) QuadraticSolution {
+        var discriminent: f128 = @floatFromInt(self.b * self.b - 4 * self.a * self.c);
+
+        var floatA: f128 = @floatFromInt(self.a);
+        var floatB: f128 = @floatFromInt(self.b);
+
+        var x_1 = (-floatB + @sqrt(discriminent)) / (2 * floatA);
+        var x_2 = (-floatB - @sqrt(discriminent)) / (2 * floatA);
+
+        return QuadraticSolution{
+            .x1 = x_1,
+            .x2 = x_2,
+        };
+    }
+};
+
+pub fn solve(input: [][]const u8) !void {
+    var allocator = std.heap.page_allocator;
+
+    var timeTokens = std.mem.tokenizeSequence(u8, input[0], " ");
+    var distanceTokens = std.mem.tokenizeSequence(u8, input[1], " ");
+
+    _ = timeTokens.next().?;
+    _ = distanceTokens.next().?;
+
+    var times = try allocator.alloc(i128, 4);
+    var distances = try allocator.alloc(i128, 4);
+
+    times[3] = 0;
+
+    var stringTime = try allocator.alloc(u8, 100);
+    var stringDistance = try allocator.alloc(u8, 100);
+
+    defer allocator.free(stringTime);
+    defer allocator.free(stringDistance);
+
+    var index: usize = 0;
+    var k: usize = 0;
+    var j: usize = 0;
+
+    while (timeTokens.next()) |time| {
+        for (0..time.len) |_k| {
+            stringTime[k] = time[_k];
+            k += 1;
+        }
+
+        times[index] = try std.fmt.parseInt(i128, time, 10);
+
+        var distance = distanceTokens.next().?;
+
+        for (0..distance.len) |_k| {
+            stringDistance[j] = distance[_k];
+            j += 1;
+        }
+
+        distances[index] = try std.fmt.parseInt(i128, distance, 10);
+        index += 1;
+    }
+
+    if (times[3] == 0) {
+        // example input
+        _ = allocator.resize(times, 3);
+        _ = allocator.resize(distances, 3);
+
+        var timesCopy = try allocator.alloc(i128, 3);
+        var distanceCopy = try allocator.alloc(i128, 3);
+
+        timesCopy[0] = times[0];
+        timesCopy[1] = times[1];
+        timesCopy[2] = times[2];
+
+        distanceCopy[0] = distances[0];
+        distanceCopy[1] = distances[1];
+        distanceCopy[2] = distances[2];
+
+        allocator.free(times);
+        allocator.free(distances);
+
+        times = timesCopy;
+        distances = distanceCopy;
+    }
+
+    var part1: u32 = 1;
+
+    for (0..times.len) |i| {
+        var quad = Quadratic{ .a = -1, .b = times[i], .c = -distances[i] };
+        var solution = quad.solve();
+        var start: u32 = @intFromFloat(math.ceil(solution.x1));
+        var end: u32 = @intFromFloat(math.floor(solution.x2));
+
+        if (@mod(solution.x2, 1) == 0) {
+            end -= 1;
+        } else {
+            end += 1;
+        }
+
+        part1 *= end - start;
+    }
+
+    print("Part 1: {}\n", .{part1});
+
+    var part2Time = try std.fmt.parseInt(i128, stringTime[0..k], 10);
+    var part2Distance = try std.fmt.parseInt(i128, stringDistance[0..j], 10);
+
+    var quad = Quadratic{ .a = -1, .b = part2Time, .c = -part2Distance };
+    var solution = quad.solve();
+    var start: usize = @intFromFloat(math.ceil(solution.x1));
+    var end: usize = @intFromFloat(math.floor(solution.x2));
+
+    if (@mod(solution.x2, 1) == 0) {
+        end -= 1;
+    } else {
+        end += 1;
+    }
+
+    var part2 = end - start;
+
+    print("Part 2: {}\n", .{part2});
+}
diff --git a/AdventOfCode2023/src/main.zig b/AdventOfCode2023/src/main.zig
index aec1c5b..5d28e3a 100644
--- a/AdventOfCode2023/src/main.zig
+++ b/AdventOfCode2023/src/main.zig
@@ -3,13 +3,14 @@ const std = @import("std");
 // const day2 = @import("./day2/day2.zig");
 // const day3 = @import("./day3/day3.zig");
 // const day4 = @import("./day4/day4.zig");
-const day5 = @import("./day5/day5.zig");
+// const day5 = @import("./day5/day5.zig");
+const day6 = @import("./day6/day6.zig");
 const utils = @import("utils.zig");
 
 pub fn main() !void {
     const allocator = std.heap.page_allocator;
-    var input = try utils.getInput("./src/day5/input.txt", allocator);
+    var input = try utils.getInput("./src/day6/input.txt", allocator);
     defer allocator.free(input);
 
-    try day5.solve(input);
+    try day6.solve(input);
 }