From: Brendan Hansen <brendan.f.hansen@gmail.com>
Date: Fri, 25 Dec 2020 15:24:25 +0000 (-0600)
Subject: added day 25
X-Git-Url: https://git.brendanfh.com/?a=commitdiff_plain;h=11d9c08ab33de197fa4e21c47ef57dcd1dd99508;p=onyx-aoc-2020.git

added day 25
---

diff --git a/day24.onyx b/day24.onyx
index cc86d31..9484642 100644
--- a/day24.onyx
+++ b/day24.onyx
@@ -68,14 +68,14 @@ main :: proc (args: [] cstr) {
 		}
 
 
-		curr := map.get(^grid, loc, Cell.{});	
+		curr := map.get(^grid, loc, Cell.{});
 		map.put(^grid, loc, Cell.{ alive = !curr.alive });
 	}
 
 	// Part 1
 	black_count := 0;
-	for tile_entry: grid.entries {
-		if tile_entry.value.alive do black_count += 1;
+	for ^cell: grid.entries {
+		if cell.value.alive do black_count += 1;
 	}	
 	printf("Black count: %i\n", black_count);
 
@@ -112,17 +112,15 @@ main :: proc (args: [] cstr) {
 		}
 
 		for ^cell: cells_to_consider {
-			state := map.get(^grid, *cell, Cell.{});
-			state.alive = state.next;
-			map.put(^grid, *cell, state);	
+			map.update(^grid, *cell, proc (state: ^Cell) { state.alive = state.next; });
 		}
 
 		array.clear(^cells_to_consider);
 	}
 
 	black_count = 0;
-	for tile_entry: grid.entries {
-		if tile_entry.value.alive do black_count += 1;
+	for ^cell: grid.entries {
+		if cell.value.alive do black_count += 1;
 	}	
 	printf("GOL black count: %i\n", black_count);
 }
diff --git a/day25.onyx b/day25.onyx
new file mode 100644
index 0000000..bf7e1af
--- /dev/null
+++ b/day25.onyx
@@ -0,0 +1,74 @@
+#include_file "core/std/wasi"
+
+use package core
+use package core.string.reader as reader
+
+power_mod :: proc (base: u32, exp: u32, mod: u32) -> u32 {
+    t: u64 = 1;
+    e: u64 = ~~exp;
+    b: u64 = ~~base;
+    m: u64 = ~~mod;
+
+    while e > 0 {
+        if e % 2 != 0 do t = (t * b) % m;
+
+        b = (b * b) % m;
+        e /= 2;
+    }
+
+    return ~~(t % m);
+}
+
+dlp_bsgs :: proc (n: u32, a: u32, b: u32) -> u32 {
+    use package core.intrinsics.wasm { ceil_f64, sqrt_f64 }
+
+    m := cast(u32) ceil_f64(sqrt_f64(~~n));
+
+    t : map.Map(u32, u32);
+    map.init(^t, m / 2);
+    defer map.free(^t);
+
+    tmp: u64 = 1;
+    for i: 0 .. m {
+        map.put(^t, ~~tmp, i);
+        tmp = (tmp * ~~a) % ~~n;
+    }
+
+    f := power_mod(a, n - 1 - m, n);
+
+    tmp = ~~b;
+    for i: 0 .. m {
+        if map.has(^t, cast(u32) tmp) {
+            v := map.get(^t, cast(u32) tmp, 0);
+            return i * m + v; 
+        }
+
+        tmp = (tmp * ~~f) % ~~n;
+    }
+
+    return 0;
+}
+
+transform_subject :: proc (subject: u32, loop_size: u32) -> u32 {
+    value: u64 = 1;
+    for i: 0 .. loop_size do value = (value * ~~subject) % 20201227;
+    return cast(u32) value;
+}
+
+main :: proc (args: [] cstr) {
+    contents := file.get_contents("input/day25.txt");
+    defer string.free(contents);
+
+    file := reader.make(contents);
+
+    card_pub_key := reader.read_u32(^file);
+    door_pub_key := reader.read_u32(^file);
+
+    card_loop_secret := dlp_bsgs(20201227, 7, card_pub_key);
+    door_loop_secret := dlp_bsgs(20201227, 7, door_pub_key);
+
+    encryption_key_0 := transform_subject(door_pub_key, card_loop_secret);
+    encryption_key_1 := transform_subject(card_pub_key, door_loop_secret);
+
+    printf("%i == %i\n", encryption_key_0, encryption_key_1);
+}
diff --git a/input/day25.txt b/input/day25.txt
new file mode 100644
index 0000000..4b4f611
--- /dev/null
+++ b/input/day25.txt
@@ -0,0 +1,2 @@
+12092626
+4707356