diff --git a/day10.zig b/day10.zig
new file mode 100644
index 0000000..656012a
--- /dev/null
+++ b/day10.zig
@@ -0,0 +1,361 @@
+const std = @import("std");
+
+const utils = @import("lib/utils.zig");
+
+const spice = @import("lib/spice.zig");
+
+const filename = "inputs/day10.txt";
+
+pub fn main() !void {
+    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+    const alloc = gpa.allocator();
+
+    {
+        const file_reader = try utils.FileReader.init(alloc, filename);
+        defer file_reader.deinit();
+
+        const result = try part1(alloc, file_reader.reader());
+
+        try std.io.getStdOut().writer().print("Day 10, part 1: {}\n", .{result});
+    }
+
+    {
+        const file_reader = try utils.FileReader.init(alloc, filename);
+        defer file_reader.deinit();
+
+        const result = try part2(alloc, file_reader.reader());
+
+        try std.io.getStdOut().writer().print("Day 10, part 2: {}\n", .{result});
+    }
+}
+
+const Pos = struct {
+    x: i32,
+    y: i32,
+};
+
+const Map = struct {
+    size_x: u32,
+    size_y: u32,
+
+    map: []const []const u8,
+
+    pub fn format(self: Map, comptime fmt: []const u8, options: std.fmt.FormatOptions, writer: anytype) !void {
+        _ = fmt;
+        _ = options;
+
+        for (self.map) |line| {
+            for (line) |x| {
+                try writer.print("{} ", .{x});
+            }
+
+            _ = try writer.write("\n");
+        }
+    }
+
+    fn get(self: Map, x: i32, y: i32) ?u8 {
+        if (x < 0 or x >= @as(i32, @intCast(self.size_x)) or y < 0 or y >= @as(i32, @intCast(self.size_y))) {
+            return null;
+        }
+
+        return self.map[@intCast(x)][@intCast(y)];
+    }
+};
+
+fn findAllEnds(ends: *std.AutoHashMap(Pos, void), map: Map, start_pos: Pos) !void {
+    const findAllEndsRec = struct {
+        fn findAllEndsRec(_ends: *std.AutoHashMap(Pos, void), _map: Map, cur_pos: Pos, height: u8) !void {
+            const cur_x = cur_pos.x;
+            const cur_y = cur_pos.y;
+
+            std.debug.assert(_map.get(cur_x, cur_y).? == height);
+
+            if (height == 9) {
+                try _ends.put(cur_pos, {});
+
+                return;
+            }
+
+            {
+                const new_x = cur_x - 1;
+                const new_y = cur_y;
+
+                if (_map.get(new_x, new_y)) |new_height| {
+                    if (new_height == height + 1) {
+                        try findAllEndsRec(_ends, _map, .{ .x = new_x, .y = new_y }, new_height);
+                    }
+                }
+            }
+
+            {
+                const new_x = cur_x + 1;
+                const new_y = cur_y;
+
+                if (_map.get(new_x, new_y)) |new_height| {
+                    if (new_height == height + 1) {
+                        try findAllEndsRec(_ends, _map, .{ .x = new_x, .y = new_y }, new_height);
+                    }
+                }
+            }
+
+            {
+                const new_x = cur_x;
+                const new_y = cur_y - 1;
+
+                if (_map.get(new_x, new_y)) |new_height| {
+                    if (new_height == height + 1) {
+                        try findAllEndsRec(_ends, _map, .{ .x = new_x, .y = new_y }, new_height);
+                    }
+                }
+            }
+
+            {
+                const new_x = cur_x;
+                const new_y = cur_y + 1;
+
+                if (_map.get(new_x, new_y)) |new_height| {
+                    if (new_height == height + 1) {
+                        try findAllEndsRec(_ends, _map, .{ .x = new_x, .y = new_y }, new_height);
+                    }
+                }
+            }
+        }
+    }.findAllEndsRec;
+
+    try findAllEndsRec(ends, map, start_pos, 0);
+}
+
+fn countAllTrails(map: Map, start_pos: Pos) !u64 {
+    const countAllTrailsRec = struct {
+        fn countAllTrailsRec(_map: Map, cur_pos: Pos, height: u8) !u64 {
+            const cur_x = cur_pos.x;
+            const cur_y = cur_pos.y;
+
+            std.debug.assert(_map.get(cur_x, cur_y).? == height);
+
+            if (height == 9) {
+                return 1;
+            }
+
+            var count: u64 = 0;
+
+            {
+                const new_x = cur_x - 1;
+                const new_y = cur_y;
+
+                if (_map.get(new_x, new_y)) |new_height| {
+                    if (new_height == height + 1) {
+                        count += try countAllTrailsRec(_map, .{ .x = new_x, .y = new_y }, new_height);
+                    }
+                }
+            }
+
+            {
+                const new_x = cur_x + 1;
+                const new_y = cur_y;
+
+                if (_map.get(new_x, new_y)) |new_height| {
+                    if (new_height == height + 1) {
+                        count += try countAllTrailsRec(_map, .{ .x = new_x, .y = new_y }, new_height);
+                    }
+                }
+            }
+
+            {
+                const new_x = cur_x;
+                const new_y = cur_y - 1;
+
+                if (_map.get(new_x, new_y)) |new_height| {
+                    if (new_height == height + 1) {
+                        count += try countAllTrailsRec(_map, .{ .x = new_x, .y = new_y }, new_height);
+                    }
+                }
+            }
+
+            {
+                const new_x = cur_x;
+                const new_y = cur_y + 1;
+
+                if (_map.get(new_x, new_y)) |new_height| {
+                    if (new_height == height + 1) {
+                        count += try countAllTrailsRec(_map, .{ .x = new_x, .y = new_y }, new_height);
+                    }
+                }
+            }
+
+            return count;
+        }
+    }.countAllTrailsRec;
+
+    return try countAllTrailsRec(map, start_pos, 0);
+}
+
+fn part1(alloc: std.mem.Allocator, reader: anytype) !u64 {
+    var map_arena = std.heap.ArenaAllocator.init(alloc);
+    defer map_arena.deinit();
+
+    var map_list = std.ArrayList([]const u8).init(map_arena.allocator());
+    defer map_list.deinit();
+
+    var line_reader = utils.lineReader(alloc, reader);
+    defer line_reader.deinit();
+
+    while (try line_reader.next()) |line| {
+        const map_line = try map_arena.allocator().alloc(u8, line.len);
+
+        for (line, map_line) |c, *x| {
+            std.debug.assert('0' <= c and c <= '9');
+
+            x.* = c - '0';
+        }
+
+        try map_list.append(map_line);
+    }
+
+    const size_x = map_list.items.len;
+    const size_y = map_list.items[0].len;
+
+    for (map_list.items) |line| {
+        std.debug.assert(line.len == size_y);
+    }
+
+    const map = Map{ .size_x = @intCast(size_x), .size_y = @intCast(size_y), .map = map_list.items };
+
+    var count: u64 = 0;
+
+    var ends = std.AutoHashMap(Pos, void).init(alloc);
+    defer ends.deinit();
+
+    for (0..size_x) |x| {
+        for (0..size_y) |y| {
+            if (map.get(@intCast(x), @intCast(y)) != 0) {
+                continue;
+            }
+
+            ends.clearRetainingCapacity();
+
+            try findAllEnds(&ends, map, .{ .x = @intCast(x), .y = @intCast(y) });
+
+            count += @intCast(ends.count());
+        }
+    }
+
+    return count;
+}
+
+fn part2(alloc: std.mem.Allocator, reader: anytype) !u64 {
+    var map_arena = std.heap.ArenaAllocator.init(alloc);
+    defer map_arena.deinit();
+
+    var map_list = std.ArrayList([]const u8).init(map_arena.allocator());
+    defer map_list.deinit();
+
+    var line_reader = utils.lineReader(alloc, reader);
+    defer line_reader.deinit();
+
+    while (try line_reader.next()) |line| {
+        const map_line = try map_arena.allocator().alloc(u8, line.len);
+
+        for (line, map_line) |c, *x| {
+            std.debug.assert('0' <= c and c <= '9');
+
+            x.* = c - '0';
+        }
+
+        try map_list.append(map_line);
+    }
+
+    const size_x = map_list.items.len;
+    const size_y = map_list.items[0].len;
+
+    for (map_list.items) |line| {
+        std.debug.assert(line.len == size_y);
+    }
+
+    const map = Map{ .size_x = @intCast(size_x), .size_y = @intCast(size_y), .map = map_list.items };
+
+    var count: u64 = 0;
+
+    var ends = std.AutoHashMap(Pos, void).init(alloc);
+    defer ends.deinit();
+
+    for (0..size_x) |x| {
+        for (0..size_y) |y| {
+            if (map.get(@intCast(x), @intCast(y)) != 0) {
+                continue;
+            }
+
+            ends.clearRetainingCapacity();
+
+            const num_trails = try countAllTrails(map, .{ .x = @intCast(x), .y = @intCast(y) });
+
+            count += num_trails;
+        }
+    }
+
+    return count;
+}
+
+test "part1 example" {
+    const alloc = std.testing.allocator;
+
+    const example =
+        \\89010123
+        \\78121874
+        \\87430965
+        \\96549874
+        \\45678903
+        \\32019012
+        \\01329801
+        \\10456732
+    ;
+
+    var stream = std.io.fixedBufferStream(example);
+
+    const result = try part1(alloc, stream.reader());
+
+    try std.testing.expectEqual(36, result);
+}
+
+test "part1 input" {
+    const alloc = std.testing.allocator;
+
+    const file_reader = try utils.FileReader.init(alloc, filename);
+    defer file_reader.deinit();
+
+    const result = try part1(alloc, file_reader.reader());
+
+    try std.testing.expectEqual(629, result);
+}
+
+test "part2 example" {
+    const alloc = std.testing.allocator;
+
+    const example =
+        \\89010123
+        \\78121874
+        \\87430965
+        \\96549874
+        \\45678903
+        \\32019012
+        \\01329801
+        \\10456732
+    ;
+
+    var stream = std.io.fixedBufferStream(example);
+
+    const result = try part2(alloc, stream.reader());
+
+    try std.testing.expectEqual(81, result);
+}
+
+test "part2 input" {
+    const alloc = std.testing.allocator;
+
+    const file_reader = try utils.FileReader.init(alloc, filename);
+    defer file_reader.deinit();
+
+    const result = try part2(alloc, file_reader.reader());
+
+    try std.testing.expectEqual(1242, result);
+}
diff --git a/day9.zig b/day9.zig
index 89ea072..506c47b 100644
--- a/day9.zig
+++ b/day9.zig
@@ -16,7 +16,7 @@ pub fn main() !void {
 
         const result = try part1(alloc, file_reader.reader());
 
-        try std.io.getStdOut().writer().print("Day 8, part 1: {}\n", .{result});
+        try std.io.getStdOut().writer().print("Day 9, part 1: {}\n", .{result});
     }
 
     {
@@ -25,7 +25,7 @@ pub fn main() !void {
 
         const result = try part2(alloc, file_reader.reader());
 
-        try std.io.getStdOut().writer().print("Day 8, part 2: {}\n", .{result});
+        try std.io.getStdOut().writer().print("Day 9, part 2: {}\n", .{result});
     }
 }
 
diff --git a/inputs/day10.txt b/inputs/day10.txt
new file mode 100644
index 0000000..d03803e
--- /dev/null
+++ b/inputs/day10.txt
@@ -0,0 +1,50 @@
+56760198543405456770107687012987873265430701234123
+47891087612514320889298596543236982176321878985054
+30932912503423411978321436760145453089490965076567
+21043803498598502565450345897896334569584324105498
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+60234211205423469109695210567345023456987101232569
+71454301312345678100556501051269010787832198543478
+82365985407856743291447892340178732696949037643323
+99878876556989856782332309650065341054658743252110
+12389565445845698943221218761234456565789650167087
+03458890330532787892100321052442787074656782108996
+12766721221621056521098478934321692183245891210105
+00875437876521245430167569035630013290194300121234
+21980356985430130101456122128754324389980215432101
+32341245234561221212340033439961015671271326990123
+41239832101676678703121542345872343760362347887654
+50146701098787569254035671096112654854454558943210
+69655410889693452164549389987003569943003967656787
+78789324989582543076678432176124578752112876545490
+49670123476451001289986581065437669801198743454321
+34565404560302654345677893034458954321034652345210
+21670313401212701238766732123361056700125601216787
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+87690433210154901234587565078980110925643212456730
+98521049873269100448996652169765223434756965569821
+83430656794378234567385543258894304589807874321034
+12345690185123247855434789043210113676212981012125
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+50125613410030012127763019831021998568903210345692
+23498701322147897898892123742340867478912653210789
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+01678123402110995437658766789210676211010892234109
+67569016567021874378941043212101245432346781103201
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+31012365125643812898765410378876543233458216568758
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+45656189654323011056769894672145632347012674212147
+01218088745896522349850123283034701456981065100238
+14309893236787631438943210190129892123672578921109
+25456782101896540127654301012010181034543465433212