day 15 pt 2

jthatch · jthatch · commit b80d76b7ed11 · 2021-10-25T22:41:37.000+01:00
diff --git a/Makefile b/Makefile
@@ -90,7 +90,7 @@ ifeq ($(shell docker image inspect $(image-name) > /dev/null 2>&1 || echo not_ex
 	make run
 else
 ifneq ("$(wildcard vendor)", "")
-	@$(DOCKER_RUN_PHP_MY_IMAGE) $(image-name) php -dopcache.enable_cli=1 -dopcache.jit_buffer_size=100M -dopcache.jit=1255 run.php $(onlyThis)
+	@$(DOCKER_RUN_PHP_MY_IMAGE) $(image-name) php -dmemory_limit=4G -dopcache.enable_cli=1 -dopcache.jit_buffer_size=100M -dopcache.jit=1255 run.php $(onlyThis)
 else
 	@echo -e "\nFirst run detected! No vendor/ folder found, running composer update...\n"
 	make composer
diff --git a/src/Day15.php b/src/Day15.php
@@ -10,8 +10,6 @@ class Day15 extends DayBehaviour implements DayInterface
 {
     public function solvePart1(): int|string|null
     {
-        //$this->input[0] = '0,3,6';
-        //$this->input[0] = '3,1,2';
         $turns = array_map('intval', str_getcsv(trim($this->input[0])));
         $max   = 2020;
         $i     = count($turns);
@@ -33,7 +31,35 @@ public function solvePart1(): int|string|null
 
     public function solvePart2(): int|string|null
     {
-        // TODO: Implement solvePart2() method.
-        return null;
+        // this takes 12s and uses 1.42gb of memory!
+        //return 1065;
+        $turns = array_map('intval', str_getcsv(trim($this->input[0])));
+        $max   = 30000000;
+        $i     = count($turns);
+
+        // <no => [turn2,turn1]>
+        $mem  = [];
+        $last = 0;
+        // seed with starting numbers, turn always starts from 1
+        foreach ($turns as $k => $t) {
+            $mem[$t] = [$k + 1];
+            $last    = $t;
+        }
+
+        while ($i < $max) {
+            // loop backwards from end of array
+            if (1 === count($mem[$last])) {
+                $next = 0;
+            } else {
+                $next       = $mem[$last][1] - $mem[$last][0];
+                $mem[$last] = array_slice($mem[$last], -2);
+            }
+            $mem[$next][] = $i + 1;
+            $mem[$next]   = array_slice($mem[$next], -2);
+            $last         = $next;
+            ++$i;
+        }
+
+        return $last;
     }
 }
diff --git a/tests/Day15Test.php b/tests/Day15Test.php
@@ -17,5 +17,5 @@
 
 test('solves part2')
     ->expect(fn () => $this->day->solvePart2())
-    ->toBe(null)
+    ->toBe(1065)
 ;

Original file line number	Diff line number	Diff line change
`@@ -17,5 +17,5 @@`
`17`	`17`
`18`	`18`	`test('solves part2')`
`19`	`19`	`->expect(fn () => $this->day->solvePart2())`
`20`		`- ->toBe(null)`
	`20`	`+ ->toBe(1065)`
`21`	`21`	`;`