day 9

09/src/main.zig

@@ -0,0 +1,159 @@
+// okay zig is fine. ig.
+// i'm just bad at code, almost all the problems this time were
+// logic errors, not just me trying to figure the language out
+
+const std = @import("std");
+
+var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
+const alloc = arena.allocator();
+
+const test_data = @embedFile("test");
+const input_data = @embedFile("input");
+
+pub fn main() !void {
+    const stdout = std.io.getStdOut().writer();
+
+    const value1 = try run1(input_data);
+    try stdout.print("{d}\n", .{value1});
+
+    const value2 = try run2(input_data);
+    try stdout.print("{d}\n", .{value2});
+}
+
+test "test input part 1" {
+    std.debug.print("\n", .{});
+    const value = try run1(test_data);
+    std.debug.print("{d}\n", .{value});
+    try std.testing.expectEqual(1928, value);
+}
+
+test "test input part 2" {
+    std.debug.print("\n",.{});
+    const value = try run2(test_data);
+    std.debug.print("{d}\n", .{value});
+    try std.testing.expectEqual(2858, value);
+}
+
+fn parseIntFromReader(reader: anytype) anyerror!u64 {
+    const f = try reader.readByte();
+    if (f < '0' or f > '9') return error.BadCharacter;
+    var v: u64 = f - '0';
+    while (true) {
+        const c = try reader.readByte();
+        if (c < '0' or c > '9') {
+            break;
+        } else {
+            v = (v * 10) + (c - '0');
+        }
+    }
+    return v;
+}
+
+// messy
+fn run2(input: []const u8) !u64 {
+    var copy = std.ArrayList(u8).init(alloc);
+    try copy.appendSlice(input);
+    var s = copy.items;
+    var last_nonzero = s.len-1;
+    if (last_nonzero&1==1) last_nonzero -= 1;
+    var start: usize = 0;
+    var position: usize = 0;
+    var total: u64 = 0;
+    var used_l = std.ArrayList(u8).init(alloc);
+    try used_l.appendNTimes('0', s.len);
+    var used = used_l.items;
+    while (start < s.len) {
+        // s[start] is used blocks
+        used: {
+            if (s[start] == '0') {
+                const endpos = position + used[start] - '0';
+                while (position < endpos) : (position += 1) {
+                }
+                break :used;
+            }
+            const endpos = position + s[start] - '0';
+            const id = start/2;
+            while (position < endpos) : (position += 1) {
+                total += position * id;
+            }
+        }
+
+        // s[start] is free blocks
+        start += 1;
+        free: { if (start < last_nonzero) {
+            const endpos = position + s[start] - '0';
+            while (position < endpos) {
+                const rem_size = endpos - position + '0';
+                // s[last_nonzero] is last used blocks
+                var t = last_nonzero;
+                while (s[t] == '0') { t -= 2; last_nonzero -= 2; }
+                while (s[t] == '0' or (s[t] > rem_size and t > start)) { t -= 2; }
+                if (t <= start) { 
+                    for ('0'..rem_size) |_| {
+                    }
+                    position = endpos;
+                    break :free;
+                }
+                const id = t/2;
+                const this_endpos = position + s[t] - '0';
+                while (position < this_endpos) : (position += 1) {
+                    total += position * id;
+                }
+                used[t] = s[t];
+                s[t] = '0';
+            }
+        } }
+
+        // next used block
+        start += 1;
+    }
+
+    return total;
+}
+
+fn run1(input: []const u8) !u64 {
+    var copy = std.ArrayList(u8).init(alloc);
+    try copy.appendSlice(input);
+    var s = copy.items;
+    var start: usize = 0;
+    var end: usize = s.len-1;
+    if (end&1==1) end -= 1;
+    var position: usize = 0;
+    var total: u64 = 0;
+    calc: while (start < end) {
+        // s[start] is used blocks
+        {
+            const endpos = position + s[start] - '0';
+            const id = start/2;
+            while (position < endpos) : (position += 1) {
+                total += position * id;
+            }
+        }
+
+        // s[start] is free blocks
+        start += 1;
+        {
+            const endpos = position + s[start] - '0';
+            // s[end] is last used blocks
+            var id = end/2;
+            while (position < endpos) : (position += 1) {
+                while (s[end] == '0') { end -= 2; id -= 1; if (end < start) break :calc; }
+                total += position * id;
+                s[end] -= 1;
+            }
+        }
+
+        // next used block
+        start += 1;
+    }
+    // any remaining i'm lazy
+    {
+        const endpos = position + s[start] - '0';
+        const id = start/2;
+        while (position < endpos) : (position += 1) {
+            total += position * id;
+        }
+    }
+
+    return total;
+}