diff --git a/src/day05.zig b/src/day05.zig
index fd17bbc..9828ab6 100644
--- a/src/day05.zig
+++ b/src/day05.zig
@@ -30,60 +30,89 @@ const Component = struct {
     value: usize,
 };
 
+const UsizeSet = std.AutoHashMap(usize, void);
+
 fn solve(alloc: mem.Allocator, input: []const u8) !Solution {
     var it = util.splitLines(input);
     const seed_line = it.next().?;
     const seeds = try util.parseIntsScalar(usize, alloc, seed_line[mem.indexOfScalar(u8, seed_line, ':').? + 1 ..], .{});
     defer alloc.free(seeds);
-    var last_components = try std.ArrayList(Component).initCapacity(alloc, seeds.len);
-    defer last_components.deinit();
+
+    var last_values = UsizeSet.init(alloc);
+    var working_values = UsizeSet.init(alloc);
+    defer last_values.deinit();
+    defer working_values.deinit();
+
+    var low_loc: usize = std.math.maxInt(usize);
 
     var seeds_index: usize = 0;
     while (seeds_index < seeds.len) : (seeds_index += 2) {
+        last_values.clearRetainingCapacity();
+        working_values.clearRetainingCapacity();
+
+        std.debug.print("= seeding {d}/{d} =\n", .{ seeds_index, seeds.len });
         const start = seeds[seeds_index];
         const range = seeds[seeds_index + 1];
         for (start..start + range) |seed| {
-            try last_components.append(.{ .name = "seed", .value = seed });
+            // std.debug.print("seed {d}\n", .{seed});
+            try working_values.put(seed, {});
         }
-    }
 
-    var current_component: []const u8 = undefined;
-    while (it.next()) |line| {
-        if (line.len == 0) {
-            for (last_components.items, 0..) |comp, index| {
-                if (!mem.eql(u8, comp.name, current_component)) {
-                    last_components.items[index] = .{ .name = current_component, .value = comp.value };
+        // Reset parse input.
+        it = util.splitLines(input);
+        _ = it.next().?;
+        var current_component: []const u8 = undefined;
+        while (it.next()) |line| {
+            if (line.len == 0) {
+                std.debug.print("== swap ==\n", .{});
+                // Copy all remaining
+                var lv_it = last_values.iterator();
+                while (lv_it.next()) |entry| {
+                    try working_values.put(entry.key_ptr.*, {});
                 }
-            }
-        } else if (mem.endsWith(u8, line, "map:")) {
-            var t_it = util.split(line, ' ');
-            var comp_it = util.split(t_it.next().?, '-');
-            _ = comp_it.next(); // A
-            _ = comp_it.next(); // to
-            current_component = comp_it.next().?; // B
-        } else {
-            const map = try util.parseIntsScalar(usize, alloc, line, .{});
-            defer alloc.free(map);
-            // map values
-            map_blk: for (last_components.items, 0..) |comp, index| {
-                if (mem.eql(u8, comp.name, current_component)) {
-                    std.debug.print("{d} already mapped\n", .{index});
-                    continue :map_blk;
+                // Swap working sets
+                mem.swap(UsizeSet, &last_values, &working_values);
+                working_values.clearRetainingCapacity();
+            } else if (mem.endsWith(u8, line, "map:")) {
+                var t_it = util.split(line, ' ');
+                var comp_it = util.split(t_it.next().?, '-');
+                _ = comp_it.next(); // A
+                _ = comp_it.next(); // to
+                current_component = comp_it.next().?; // B
+            } else {
+                std.debug.print("== {s} {d}/{d}\n", .{ current_component, working_values.count(), last_values.count() });
+                const map = try util.parseIntsScalar(usize, alloc, line, .{});
+                defer alloc.free(map);
+
+                var to_delete = UsizeSet.init(alloc);
+                defer to_delete.deinit();
+                var lv_it = last_values.iterator();
+                while (lv_it.next()) |entry| {
+                    // if (transitioned[index]) {
+                    //     std.debug.print("{d} already mapped\n", .{index});
+                    //     continue :map_blk;
+                    // }
+                    const item = entry.key_ptr.*;
+                    if (map[1] <= item and item <= map[1] + map[2]) {
+                        const offset = @as(isize, @intCast(map[0])) - @as(isize, @intCast(map[1]));
+                        const res: usize = @intCast(@as(isize, @intCast(item)) + offset);
+                        // std.debug.print("{d} => {d}\n", .{ item, res });
+                        try working_values.put(res, {});
+                        try to_delete.put(item, {});
+                    }
                 }
-                if (map[1] <= comp.value and comp.value <= map[1] + map[2]) {
-                    const offset = @as(isize, @intCast(map[0])) - @as(isize, @intCast(map[1]));
-                    const res: usize = @intCast(@as(isize, @intCast(comp.value)) + offset);
-                    std.debug.print("{d} {d} => {d}\n", .{ index, comp.value, res });
-                    last_components.items[index] = .{ .name = current_component, .value = res };
+                var td_it = to_delete.iterator();
+                while (td_it.next()) |entry| {
+                    // std.debug.print("pop {d}\n", .{entry.key_ptr.*});
+                    _ = last_values.remove(entry.key_ptr.*);
                 }
             }
         }
-    }
 
-    var low_loc: usize = std.math.maxInt(usize);
-    for (last_components.items) |comp| {
-        std.debug.print("{s} ", .{comp.name});
-        low_loc = @min(low_loc, comp.value);
+        var lv_it = last_values.iterator();
+        while (lv_it.next()) |value| {
+            low_loc = @min(low_loc, value.key_ptr.*);
+        }
     }
 
     return .{ .a = low_loc, .b = 0 };