diff --git a/AdventOfCode2023/src/day21/day21.zig b/AdventOfCode2023/src/day21/day21.zig
index daae9bc..f74dca4 100644
--- a/AdventOfCode2023/src/day21/day21.zig
+++ b/AdventOfCode2023/src/day21/day21.zig
@@ -5,7 +5,7 @@ const ROCK = '#';
 const START = 'S';
 const GARDEN = '.';
 const STEPS = 1;
-const PART2_STEPS = 6;
+const PART2_STEPS = 50;
 
 fn printGrid(grid: [][]u8) void {
     for (grid) |row| {
@@ -154,6 +154,7 @@ pub fn solve(input: [][]const u8) !void {
             var eastCoordY = y(east) % input.len;
 
             if (grid[northCoordY][northCoordX] != ROCK) {
+                print("{} - {},{}\n", .{ north, northCoordX, northCoordY });
                 try newCurrentSteps.put(north, true);
             }
             if (grid[southCoordY][southCoordX] != ROCK) {
diff --git a/AdventOfCode2023/src/day23/day23.zig b/AdventOfCode2023/src/day23/day23.zig
new file mode 100644
index 0000000..9fd69f6
--- /dev/null
+++ b/AdventOfCode2023/src/day23/day23.zig
@@ -0,0 +1,268 @@
+const std = @import("std");
+const print = std.debug.print;
+const expect = std.testing.expect;
+
+const WALL = '#';
+
+pub fn Queue(comptime Child: type) type {
+    return struct {
+        const This = @This();
+        const Node = struct {
+            data: Child,
+            next: ?*Node,
+        };
+        gpa: std.mem.Allocator,
+        start: ?*Node,
+        end: ?*Node,
+
+        pub fn init(gpa: std.mem.Allocator) This {
+            return This{
+                .gpa = gpa,
+                .start = null,
+                .end = null,
+            };
+        }
+        pub fn enqueue(this: *This, value: Child) !void {
+            const node = try this.gpa.create(Node);
+            node.* = .{ .data = value, .next = null };
+            if (this.end) |end| end.next = node //
+            else this.start = node;
+            this.end = node;
+        }
+        pub fn dequeue(this: *This) ?Child {
+            const start = this.start orelse return null;
+            defer this.gpa.destroy(start);
+            if (start.next) |next|
+                this.start = next
+            else {
+                this.start = null;
+                this.end = null;
+            }
+            return start.data;
+        }
+    };
+}
+
+test "Hash maps as refs" {
+    var allocator = std.heap.page_allocator;
+
+    var q = Queue(*std.AutoHashMap(u128, bool)).init(allocator);
+    var m = std.AutoHashMap(u128, bool).init(allocator);
+
+    try m.put(0, true);
+    try m.put(1, true);
+    try expect(m.count() == 2);
+
+    try q.enqueue(&m);
+    var mPointer: *std.AutoHashMap(u128, bool) = q.dequeue().?;
+
+    try expect(mPointer.*.count() == 2);
+}
+
+fn coord(myX: usize, myY: usize) u128 {
+    return @as(u128, myX) << 64 | @as(u128, myY);
+}
+
+fn x(c: u128) usize {
+    return @truncate(c >> 64);
+}
+
+fn y(c: u128) usize {
+    return @truncate(c);
+}
+
+fn linear_search(arr: []u128, search: u128) bool {
+    for (arr) |i| {
+        if (i == search) {
+            return true;
+        }
+    }
+    return false;
+}
+
+fn short_copy(longerArr: []u128, shorterArr: []u128) void {
+    for (0..shorterArr.len) |i| {
+        longerArr[i] = shorterArr[i];
+    }
+}
+
+fn isStep(s: u8, want: u8) bool {
+    if (s == '.') {
+        return true;
+    }
+
+    return want == s;
+}
+
+// const Edge = struct {
+//     weight: usize,
+//     node: *Node,
+// };
+//
+// const Node = struct {
+//     edges: []?Edge,
+// };
+
+fn bfs(grid: [][]const u8, goal: u128, explored: *std.AutoHashMap(u128, bool), root: u128, allocator: std.mem.Allocator, part2: bool) !usize {
+    var q = Queue(u128).init(allocator);
+    var qLength = Queue(usize).init(allocator);
+    var qPaths = Queue([]u128).init(allocator);
+
+    try explored.*.put(root, true);
+    try q.enqueue(root);
+    try qLength.enqueue(0);
+
+    var myPaths = try allocator.alloc(u128, 2);
+
+    var keyIter = explored.keyIterator();
+    var index: usize = 0;
+    while (keyIter.next()) |key| {
+        myPaths[index] = key.*;
+        index += 1;
+    }
+
+    try qPaths.enqueue(myPaths);
+
+    var part1: usize = 0;
+
+    while (q.dequeue()) |c| {
+        var child: u128 = c;
+        var size: usize = qLength.dequeue().?;
+        var paths: []u128 = qPaths.dequeue().?;
+
+        if (child == goal) {
+            // don't return, because we need all routes.
+            print("Size: {}\n", .{size + 1});
+            part1 = size + 1;
+            continue;
+        }
+
+        var up = child - 1;
+        var upX = x(up);
+        var upY = y(up);
+
+        var down = child + 1;
+        var downX = x(down);
+        var downY = y(down);
+
+        var right = child + (@as(u128, 1) << 64);
+        var rightX = x(right);
+        var rightY = y(right);
+
+        var left = child - (@as(u128, 1) << 64);
+        var leftX = x(left);
+        var leftY = y(left);
+
+        var lastStep = paths[paths.len - 1];
+        var lastStepX = x(lastStep);
+        var lastStepY = y(lastStep);
+        var l = grid[lastStepY][lastStepX];
+        if (part2) {
+            l = '.';
+        }
+
+        if (!linear_search(paths, up) and grid[upY][upX] != WALL and isStep(l, '^')) {
+            var pathsCopy = try allocator.alloc(u128, paths.len + 1);
+            short_copy(pathsCopy, paths);
+            pathsCopy[pathsCopy.len - 1] = up;
+
+            try q.enqueue(up);
+            try qLength.enqueue(size + 1);
+            try qPaths.enqueue(pathsCopy);
+        }
+        if (!linear_search(paths, down) and grid[downY][downX] != WALL and isStep(l, 'v')) {
+            var pathsCopy = try allocator.alloc(u128, paths.len + 1);
+            short_copy(pathsCopy, paths);
+            pathsCopy[pathsCopy.len - 1] = down;
+
+            try q.enqueue(down);
+            try qLength.enqueue(size + 1);
+            try qPaths.enqueue(pathsCopy);
+        }
+        if (!linear_search(paths, right) and grid[rightY][rightX] != WALL and isStep(l, '>')) {
+            var pathsCopy = try allocator.alloc(u128, paths.len + 1);
+            short_copy(pathsCopy, paths);
+            pathsCopy[pathsCopy.len - 1] = right;
+
+            try q.enqueue(right);
+            try qLength.enqueue(size + 1);
+            try qPaths.enqueue(pathsCopy);
+        }
+        if (!linear_search(paths, left) and grid[leftY][leftX] != WALL and isStep(l, '<')) {
+            var pathsCopy = try allocator.alloc(u128, paths.len + 1);
+            short_copy(pathsCopy, paths);
+            pathsCopy[pathsCopy.len - 1] = left;
+
+            try q.enqueue(left);
+            try qLength.enqueue(size + 1);
+            try qPaths.enqueue(pathsCopy);
+        }
+
+        allocator.free(paths);
+    }
+
+    return part1;
+}
+
+fn dps(grid: [][]const u8, root: u128, goal: u128, explored: []u128, size: usize, allocator: std.mem.Allocator) !usize {
+    if (root == goal) {
+        print("Size: {}\n", .{size});
+        return size;
+    }
+
+    var up = root - 1;
+    var down = root + 1;
+    var right = root + (@as(u128, 1) << 64);
+    var left = root - (@as(u128, 1) << 64);
+    var neighbours = [_]u128{ up, down, right, left };
+
+    var highest: usize = 0;
+
+    for (neighbours) |n| {
+        var nx = x(n);
+        var ny = y(n);
+        if (!linear_search(explored, n) and grid[ny][nx] != WALL) {
+            var copyExplored = try allocator.alloc(u128, explored.len + 1);
+            short_copy(copyExplored, explored);
+            copyExplored[copyExplored.len - 1] = n;
+            var h = try dps(grid, n, goal, copyExplored, size + 1, allocator);
+            if (h > highest) {
+                highest = h;
+            }
+
+            allocator.free(copyExplored);
+        }
+    }
+
+    return highest;
+}
+
+pub fn solve(input: [][]const u8) !void {
+    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+    var allocator = gpa.allocator();
+
+    var explored = std.AutoHashMap(u128, bool).init(allocator);
+
+    var start = coord(1, 0);
+    try explored.put(start, true);
+
+    var fakeStart = coord(1, 1);
+
+    var goal = coord(input[0].len - 2, input.len - 1);
+    _ = goal;
+
+    // var part1 = try bfs(input, goal, &explored, fakeStart, allocator, false);
+    // print("Part 1: {}\n", .{part1});
+
+    // var part2 = try bfs(input, goal, &explored, fakeStart, allocator, true);
+    // print("Part 2: {}\n", .{part2});
+
+    var exp = try allocator.alloc(u128, 1);
+    exp[0] = start;
+
+    // var exampleLastInter = coord(19, 20);
+    var exampleLastInter = coord(133, 137);
+
+    var part2 = try dps(input, fakeStart, exampleLastInter, exp, 0, allocator);
+    print("Part 2: {}\n", .{part2 + 21});
+}
diff --git a/AdventOfCode2023/src/day24/day24.zig b/AdventOfCode2023/src/day24/day24.zig
new file mode 100644
index 0000000..7e53ef9
--- /dev/null
+++ b/AdventOfCode2023/src/day24/day24.zig
@@ -0,0 +1,111 @@
+const std = @import("std");
+const print = std.debug.print;
+const expect = std.testing.expect;
+
+const Line = struct {
+    x: i128,
+    y: i128,
+    z: i128,
+
+    dx: i128,
+    dy: i128,
+    dz: i128,
+
+    pub fn isNegative(self: Line) bool {
+        if (self.dx < 0 and self.dy < 0) {
+            return false;
+        }
+
+        return self.dx < 0 or self.dy < 0;
+    }
+
+    pub fn time(self: Line, point: f128) f128 {
+        var fx: f128 = @floatFromInt(self.x);
+        var fdx: f128 = @floatFromInt(self.dx);
+
+        return (point - fx) / fdx;
+    }
+};
+
+// const LOWER = 7;
+// const HIGHER = 27;
+const LOWER = 200000000000000;
+const HIGHER = 400000000000000;
+
+const Solution = struct {
+    x: f128,
+    y: f128,
+    z: f128,
+};
+
+test "Floating points" {
+    var a: i128 = 5.123;
+    var b: i128 = 5.123;
+
+    try expect(a - b == 0);
+}
+
+fn asFloat(a: i128) f128 {
+    return @as(f128, @floatFromInt(a));
+}
+
+fn linear_algebra_2d(line1: Line, line2: Line) ?Solution {
+    var m1: f128 = asFloat(line1.dy) / asFloat(line1.dx);
+    var A: f128 = asFloat(line1.y) - m1 * asFloat(line1.x);
+
+    var m2: f128 = asFloat(line2.dy) / asFloat(line2.dx);
+    var B: f128 = asFloat(line2.y) - m2 * asFloat(line2.x);
+
+    if (m1 == m2) {
+        return null;
+    }
+
+    var deltaM = m2 - m1;
+
+    var x = A / deltaM - B / deltaM;
+    var y = (A * m2) / deltaM - (B * m1) / deltaM;
+
+    return Solution{ .x = x, .y = y, .z = 0 };
+}
+
+pub fn solve(input: [][]const u8) !void {
+    var allocator = std.heap.page_allocator;
+    var lines = try allocator.alloc(Line, input.len);
+
+    for (input, 0..) |line, i| {
+        var tokenizer = std.mem.tokenizeAny(u8, line, " ,@");
+        var x = try std.fmt.parseInt(i128, tokenizer.next().?, 10);
+        var y = try std.fmt.parseInt(i128, tokenizer.next().?, 10);
+        var z = try std.fmt.parseInt(i128, tokenizer.next().?, 10);
+
+        var dx = try std.fmt.parseInt(i128, tokenizer.next().?, 10);
+        var dy = try std.fmt.parseInt(i128, tokenizer.next().?, 10);
+        var dz = try std.fmt.parseInt(i128, tokenizer.next().?, 10);
+
+        var l = Line{ .x = x, .y = y, .z = z, .dx = dx, .dy = dy, .dz = dz };
+        lines[i] = l;
+    }
+
+    var part1: usize = 0;
+
+    for (0..lines.len) |i| {
+        for (i + 1..lines.len) |j| {
+            var line1 = lines[i];
+            var line2 = lines[j];
+
+            var sol = linear_algebra_2d(line1, line2);
+            if (sol) |s| {
+                if (s.x > LOWER and s.y > LOWER and s.x < HIGHER and s.y < HIGHER) {
+                    if (line1.time(s.x) < 0 or line2.time(s.x) < 0) {
+                        continue;
+                    }
+
+                    part1 += 1;
+                }
+                continue;
+            }
+        }
+    }
+
+    print("Part 1: {}\n", .{part1});
+}
diff --git a/AdventOfCode2023/src/main.zig b/AdventOfCode2023/src/main.zig
index 5c70ce4..fb5edb8 100644
--- a/AdventOfCode2023/src/main.zig
+++ b/AdventOfCode2023/src/main.zig
@@ -14,13 +14,15 @@ const std = @import("std");
 // const day16 = @import("./day16/day16.zig");
 // const day18 = @import("./day18/day18.zig");
 // const day19 = @import("./day19/day19.zig");
-const day21 = @import("./day21/day21.zig");
+// const day21 = @import("./day21/day21.zig");
+// const day23 = @import("./day23/day23.zig");
+const day24 = @import("./day24/day24.zig");
 const utils = @import("utils.zig");
 
 pub fn main() !void {
     const allocator = std.heap.page_allocator;
-    var input = try utils.getInput("./src/day21/input.txt", allocator);
+    var input = try utils.getInput("./src/day24/input.txt", allocator);
     defer allocator.free(input);
 
-    try day21.solve(input);
+    try day24.solve(input);
 }