Add day 9

aoc2020/lib/aoc2020.dart

@@ -6,6 +6,7 @@ import 'package:aoc2020/aoc20201201.dart';
 import 'package:aoc2020/aoc20201206.dart';
 import 'package:aoc2020/aoc20201207.dart';
 import 'package:aoc2020/aoc20201208.dart';
+import 'package:aoc2020/aoc20201209.dart';
 import 'package:aoc2020/aocbase.dart';
 import 'dart:mirrors';
 
@@ -24,6 +25,7 @@ class aoc2020 {
     AOC20201206(),
     AOC20201207(),
     AOC20201208(),
+    AOC20201209(),
   ];
 
   static void list() async {

aoc2020/lib/aoc20201209.dart

@@ -2,15 +2,61 @@ import 'package:aoc2020/aocbase.dart';
 import 'package:aoc2020/model/readdata.dart';
 
 class AOC20201209 extends AOCBase {
+  int testpreamble = 5;
+  int runpreamble = 25;
+  int preamble;
+  int index;
+  var mylist = <num>[];
+
+  void init(String filename, bool test) async {
+    mylist = await ReadData.readFileNum(filename);
+    preamble = test ?? false ? testpreamble : runpreamble;
+    index = preamble;
+  }
+
+  bool testGroup(int index) {
+    var val = mylist[index];
+    var sublist = Set.from(mylist.sublist(index - preamble, index));
+    var testset = Set.from(sublist.map((elem) => val - elem));
+    return testset.intersection(sublist).isNotEmpty;
+  }
+
+  List<num> sumTest(num testcase, num start) {
+    var sum = 0;
+    var end = start;
+    var group = <num>[];
+    do {
+      end++;
+      group = mylist.sublist(start, end);
+      sum = group.fold(0, (prev, element) => prev + element);
+    } while (sum < testcase);
+    return sum == testcase ? group : [];
+  }
+
   @override
   Future<void> a({bool test}) async {
     var filename = (test ?? false) ? classStringTest : classString;
-    var mylist = await ReadData.readFileString(filename);
+    await init(filename, test);
+    for (index = preamble; index < mylist.length && testGroup(index); index++);
+    if (index < mylist.length) {
+      answerA = mylist[index];
+    } else {
+      print('past end');
+    }
   }
 
   @override
   Future<void> b({bool test}) async {
     var filename = (test ?? false) ? classStringTest : classString;
-    var mylist = await ReadData.readFileString(filename);
+    await init(filename, test);
+    index = 0;
+    for (index = 0; index < mylist.length; index++) {
+      var mysum = sumTest(answerA, index);
+      if (mysum. isNotEmpty) {
+        mysum.sort();
+        answerB = mysum.first + mysum.last;
+        break;
+      }
+    }
   }
 }

aoc2020/lib/data/aoc20201209test.data

@@ -0,0 +1,20 @@
+35
+20
+15
+25
+47
+40
+62
+55
+65
+95
+102
+117
+150
+182
+127
+219
+299
+277
+309
+576