diff --git a/AdventOfCode2023/build.zig b/AdventOfCode2023/build.zig
index e93d0fa..399b7c1 100644
--- a/AdventOfCode2023/build.zig
+++ b/AdventOfCode2023/build.zig
@@ -17,18 +17,11 @@ pub fn build(b: *std.Build) void {
 
     const exe = b.addExecutable(.{
         .name = "AdventOfCode2023",
-        // In this case the main source file is merely a path, however, in more
-        // complicated build scripts, this could be a generated file.
-        .root_source_file = .{ .path = "src/main.zig" },
+        .root_source_file = b.path("src/main.zig"),
         .target = target,
         .optimize = optimize,
     });
 
-    const utils_module = b.createModule(.{
-        .source_file = .{ .path = "src/utils.zig" },
-    });
-    exe.addModule("utils", utils_module);
-
     // This declares intent for the executable to be installed into the
     // standard location when the user invokes the "install" step (the default
     // step when running `zig build`).
@@ -60,7 +53,7 @@ pub fn build(b: *std.Build) void {
     // Creates a step for unit testing. This only builds the test executable
     // but does not run it.
     const unit_tests = b.addTest(.{
-        .root_source_file = .{ .path = "src/main.zig" },
+        .root_source_file = b.path("src/main.zig"),
         .target = target,
         .optimize = optimize,
     });
diff --git a/AdventOfCode2023/src/day23/day23.zig b/AdventOfCode2023/src/day23/day23.zig
index 9fd69f6..002b2a0 100644
--- a/AdventOfCode2023/src/day23/day23.zig
+++ b/AdventOfCode2023/src/day23/day23.zig
@@ -43,22 +43,6 @@ pub fn Queue(comptime Child: type) type {
     };
 }
 
-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);
 }
@@ -94,15 +78,6 @@ fn isStep(s: u8, want: u8) bool {
     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);
@@ -126,42 +101,41 @@ fn bfs(grid: [][]const u8, goal: u128, explored: *std.AutoHashMap(u128, bool), r
     var part1: usize = 0;
 
     while (q.dequeue()) |c| {
-        var child: u128 = c;
-        var size: usize = qLength.dequeue().?;
-        var paths: []u128 = qPaths.dequeue().?;
+        const child: u128 = c;
+        const size: usize = qLength.dequeue().?;
+        const 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);
+        const up = child - 1;
+        const upX = x(up);
+        const upY = y(up);
 
-        var down = child + 1;
-        var downX = x(down);
-        var downY = y(down);
+        const down = child + 1;
+        const downX = x(down);
+        const downY = y(down);
 
-        var right = child + (@as(u128, 1) << 64);
-        var rightX = x(right);
-        var rightY = y(right);
+        const right = child + (@as(u128, 1) << 64);
+        const rightX = x(right);
+        const rightY = y(right);
 
-        var left = child - (@as(u128, 1) << 64);
-        var leftX = x(left);
-        var leftY = y(left);
+        const left = child - (@as(u128, 1) << 64);
+        const leftX = x(left);
+        const leftY = y(left);
 
-        var lastStep = paths[paths.len - 1];
-        var lastStepX = x(lastStep);
-        var lastStepY = y(lastStep);
+        const lastStep = paths[paths.len - 1];
+        const lastStepX = x(lastStep);
+        const lastStepY = y(lastStep);
         var l = grid[lastStepY][lastStepX];
+
         if (part2) {
             l = '.';
         }
 
-        if (!linear_search(paths, up) and grid[upY][upX] != WALL and isStep(l, '^')) {
+        if (grid[upY][upX] != WALL and isStep(l, '^') and !linear_search(paths, up)) {
             var pathsCopy = try allocator.alloc(u128, paths.len + 1);
             short_copy(pathsCopy, paths);
             pathsCopy[pathsCopy.len - 1] = up;
@@ -170,7 +144,8 @@ fn bfs(grid: [][]const u8, goal: u128, explored: *std.AutoHashMap(u128, bool), r
             try qLength.enqueue(size + 1);
             try qPaths.enqueue(pathsCopy);
         }
-        if (!linear_search(paths, down) and grid[downY][downX] != WALL and isStep(l, 'v')) {
+
+        if (grid[downY][downX] != WALL and isStep(l, 'v') and !linear_search(paths, down)) {
             var pathsCopy = try allocator.alloc(u128, paths.len + 1);
             short_copy(pathsCopy, paths);
             pathsCopy[pathsCopy.len - 1] = down;
@@ -179,7 +154,8 @@ fn bfs(grid: [][]const u8, goal: u128, explored: *std.AutoHashMap(u128, bool), r
             try qLength.enqueue(size + 1);
             try qPaths.enqueue(pathsCopy);
         }
-        if (!linear_search(paths, right) and grid[rightY][rightX] != WALL and isStep(l, '>')) {
+
+        if (grid[rightY][rightX] != WALL and isStep(l, '>') and !linear_search(paths, right)) {
             var pathsCopy = try allocator.alloc(u128, paths.len + 1);
             short_copy(pathsCopy, paths);
             pathsCopy[pathsCopy.len - 1] = right;
@@ -188,7 +164,8 @@ fn bfs(grid: [][]const u8, goal: u128, explored: *std.AutoHashMap(u128, bool), r
             try qLength.enqueue(size + 1);
             try qPaths.enqueue(pathsCopy);
         }
-        if (!linear_search(paths, left) and grid[leftY][leftX] != WALL and isStep(l, '<')) {
+
+        if (grid[leftY][leftX] != WALL and isStep(l, '<') and !linear_search(paths, left)) {
             var pathsCopy = try allocator.alloc(u128, paths.len + 1);
             short_copy(pathsCopy, paths);
             pathsCopy[pathsCopy.len - 1] = left;
@@ -204,65 +181,225 @@ fn bfs(grid: [][]const u8, goal: u128, explored: *std.AutoHashMap(u128, bool), r
     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;
+const Direction = enum { up, down, right, left };
+
+fn num_of_non_wall(input: *const [][]const u8, coord1: u128, coord2: u128, coord3: u128, coord4: u128) u8 {
+    var counter: u8 = 0;
+
+    if (input.*[y(coord1)][x(coord1)] != WALL) {
+        counter += 1;
+    }
+    if (input.*[y(coord2)][x(coord2)] != WALL) {
+        counter += 1;
+    }
+    if (input.*[y(coord3)][x(coord3)] != WALL) {
+        counter += 1;
+    }
+    if (input.*[y(coord4)][x(coord4)] != WALL) {
+        counter += 1;
     }
 
-    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 };
+    return counter;
+}
 
-    var highest: usize = 0;
+fn direction(input: *const [][]const u8, explored: *std.AutoHashMap(u128, bool), up: u128, down: u128, right: u128, left: u128) Direction {
+    if (explored.get(up) == null and input.*[y(up)][x(up)] != WALL) {
+        return Direction.up;
+    }
+    if (explored.get(down) == null and input.*[y(down)][x(down)] != WALL) {
+        return Direction.down;
+    }
+    if (explored.get(left) == null and input.*[y(left)][x(left)] != WALL) {
+        return Direction.left;
+    }
+    if (explored.get(right) == null and input.*[y(right)][x(right)] != WALL) {
+        return Direction.right;
+    }
 
-    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;
+    unreachable;
+}
+
+const Edge = struct { distance: usize, to_x: usize, to_y: usize };
+
+fn compress_graph(allocator: std.mem.Allocator, input: [][]const u8) !std.AutoHashMap(u128, []Edge) {
+    var nodes = std.ArrayList(u128).init(allocator);
+    defer nodes.deinit();
+
+    for (1..input.len - 1) |y_part| {
+        for (1..input[0].len - 1) |x_part| {
+            if (input[y_part][x_part] != '.') {
+                continue;
             }
 
-            allocator.free(copyExplored);
+            const up = coord(x_part, y_part - 1);
+            const down = coord(x_part, y_part + 1);
+            const right = coord(x_part + 1, y_part);
+            const left = coord(x_part - 1, y_part);
+
+            const non_wall_count = num_of_non_wall(&input, up, down, right, left);
+            if (non_wall_count == 0 or non_wall_count == 1) {
+                unreachable;
+            }
+
+            if (non_wall_count == 2) {
+                if (input[y(up)][x(up)] != WALL and input[y(down)][x(down)] != WALL) {
+                    continue;
+                }
+
+                if (input[y(left)][x(left)] != WALL and input[y(right)][x(right)] != WALL) {
+                    continue;
+                }
+            }
+
+            try nodes.append(coord(x_part, y_part));
         }
     }
 
-    return highest;
+    var edges_map = std.AutoHashMap(u128, []Edge).init(allocator);
+
+    for (nodes.items) |a| {
+        lower: for (nodes.items) |b| {
+            if (a == b) {
+                continue;
+            }
+
+            if (x(a) == x(b)) {
+                // Check they can see each other.
+                const min_y = if (y(a) < y(b)) y(a) else y(b);
+                const max_y = if (y(a) > y(b)) y(a) else y(b);
+
+                const contains_walls = for (min_y..max_y) |counter_y| {
+                    if (input[counter_y][x(a)] == WALL) {
+                        break true;
+                    }
+                } else false;
+
+                if (contains_walls) {
+                    continue :lower;
+                }
+
+                const new_edge = Edge{ .to_x = x(b), .to_y = y(b), .distance = max_y - min_y };
+
+                if (edges_map.get(a)) |edges_arr| {
+                    var new_edges_arr = try allocator.realloc(edges_arr, edges_arr.len + 1);
+                    new_edges_arr[new_edges_arr.len - 1] = new_edge;
+
+                    try edges_map.put(a, new_edges_arr);
+                } else {
+                    var new_edges_arr = try allocator.alloc(Edge, 1);
+                    new_edges_arr[0] = new_edge;
+
+                    try edges_map.put(a, new_edges_arr);
+                }
+            }
+
+            if (y(a) == y(b)) {
+                // Check they can see each other.
+                const min_x = if (x(a) < x(b)) x(a) else x(b);
+                const max_x = if (x(a) > x(b)) x(a) else x(b);
+
+                const contains_walls = for (min_x..max_x) |counter_x| {
+                    if (input[y(a)][counter_x] == WALL) {
+                        break true;
+                    }
+                } else false;
+
+                if (contains_walls) {
+                    continue :lower;
+                }
+
+                const new_edge = Edge{ .to_x = x(b), .to_y = y(b), .distance = max_x - min_x };
+
+                if (edges_map.get(a)) |edges_arr| {
+                    var new_edges_arr = try allocator.realloc(edges_arr, edges_arr.len + 1);
+                    new_edges_arr[new_edges_arr.len - 1] = new_edge;
+
+                    try edges_map.put(a, new_edges_arr);
+                } else {
+                    var new_edges_arr = try allocator.alloc(Edge, 1);
+                    new_edges_arr[0] = new_edge;
+
+                    try edges_map.put(a, new_edges_arr);
+                }
+            }
+        }
+    }
+
+    return edges_map;
+}
+
+fn includes(nodes: []u128, node: u128) bool {
+    for (nodes) |n| {
+        if (n == node) {
+            return true;
+        }
+    }
+
+    return false;
+}
+
+fn dfs(allocator: std.mem.Allocator, edges_map: std.AutoHashMap(u128, []Edge), end: u128) !usize {
+    var stack = std.ArrayList(u128).init(allocator);
+    var stack_distance = std.ArrayList(usize).init(allocator);
+    var stack_explored = std.ArrayList([]u128).init(allocator);
+
+    defer stack.deinit();
+    defer stack_distance.deinit();
+    defer stack_explored.deinit();
+
+    const initial_explored = try allocator.alloc(u128, 0);
+
+    try stack.append(coord(1, 1));
+    try stack_distance.append(2);
+    try stack_explored.append(initial_explored);
+
+    var longest_distance: usize = 0;
+
+    while (stack.items.len > 0) {
+        const popped_node = stack.pop();
+        const popped_distance = stack_distance.pop();
+        const popped_explored = stack_explored.pop();
+
+        defer allocator.free(popped_explored);
+
+        if (includes(popped_explored, popped_node)) {
+            continue;
+        }
+
+        if (popped_node == end and popped_distance > longest_distance) {
+            longest_distance = popped_distance;
+        }
+
+        const edges = edges_map.get(popped_node).?;
+        for (edges) |edge| {
+            var copied_edges = try allocator.alloc(u128, popped_explored.len + 1);
+            std.mem.copyForwards(u128, copied_edges, popped_explored);
+            copied_edges[copied_edges.len - 1] = popped_node;
+
+            try stack.append(coord(edge.to_x, edge.to_y));
+            try stack_distance.append(popped_distance + edge.distance);
+            try stack_explored.append(copied_edges);
+        }
+    }
+
+    return longest_distance;
 }
 
 pub fn solve(input: [][]const u8) !void {
     var gpa = std.heap.GeneralPurposeAllocator(.{}){};
-    var allocator = gpa.allocator();
+    const allocator = gpa.allocator();
 
     var explored = std.AutoHashMap(u128, bool).init(allocator);
 
-    var start = coord(1, 0);
+    const start = coord(1, 0);
     try explored.put(start, true);
 
-    var fakeStart = coord(1, 1);
+    const goal = coord(input[0].len - 2, input.len - 2);
 
-    var goal = coord(input[0].len - 2, input.len - 1);
-    _ = goal;
-
-    // var part1 = try bfs(input, goal, &explored, fakeStart, allocator, false);
+    // const 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});
+    const edges = try compress_graph(allocator, input);
+    const part2 = try dfs(allocator, edges, goal);
+    print("Part 2: {}\n", .{part2});
 }
diff --git a/AdventOfCode2023/src/main.zig b/AdventOfCode2023/src/main.zig
index af0565e..b21518b 100644
--- a/AdventOfCode2023/src/main.zig
+++ b/AdventOfCode2023/src/main.zig
@@ -19,15 +19,15 @@ const std = @import("std");
 // const day19 = @import("./day19/day19.zig");
 // const day20 = @import("./day20/day20.zig");
 // const day21 = @import("./day21/day21.zig");
-const day22 = @import("./day22/day22.zig");
-// const day23 = @import("./day23/day23.zig");
+// const day22 = @import("./day22/day22.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;
-    const input = try utils.getInput("./src/day22/input.txt", allocator);
+    const input = try utils.getInput("./src/day23/input.txt", allocator);
     defer allocator.free(input);
 
-    try day22.solve(input);
+    try day23.solve(input);
 }