Day02: Solved

lib/day02.dart

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+// --- Day 2: Red-Nosed Reports ---
+// https://adventofcode.com/2024/day/2
+
+int solveA(Iterable<String> input) =>
+    input.map((line) => line.split(' ').map(int.parse)).where(isValid).length;
+
+int solveB(Iterable<String> input) =>
+    input.map((line) => line.split(' ').map(int.parse)).where((report) {
+      if (isValid(report)) {
+        return true;
+      }
+
+      for (var i = 0; i < report.length; i++) {
+        if (isValid(report, skipLevel: i)) {
+          return true;
+        }
+      }
+
+      return false;
+    }).length;
+
+bool isValid(Iterable<int> levels, {int skipLevel = -1}) {
+  int? lastValue;
+  bool? increasing;
+
+  for (final (index, value) in levels.indexed) {
+    if (index == skipLevel) {
+      continue;
+    }
+
+    if (lastValue == null) {
+      lastValue = value;
+      continue;
+    }
+
+    if ((value - lastValue).abs() > 3 || value == lastValue) {
+      return false;
+    }
+
+    if (increasing == null) {
+      increasing = value > lastValue;
+      lastValue = value;
+      continue;
+    }
+
+    if (increasing && value < lastValue || !increasing && value > lastValue) {
+      return false;
+    }
+
+    lastValue = value;
+  }
+
+  return true;
+}

test/day02_test.dart

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+// --- Day 2: Red-Nosed Reports ---
+// https://adventofcode.com/2024/day/2
+
+import 'dart:io';
+import 'package:advent_of_code_2024/day02.dart';
+import 'package:advent_of_code_2024/util.dart';
+import 'package:test/test.dart';
+
+final input = File('test/data/day02.txt').readAsLinesSync();
+
+void main() {
+  group('Part One', () {
+    test('Example 1', () {
+      expect(
+          solveA(r'''
+7 6 4 2 1
+1 2 7 8 9
+9 7 6 2 1
+1 3 2 4 5
+8 6 4 4 1
+1 3 6 7 9
+'''
+              .asLines),
+          equals(2));
+    });
+    test('Solution', () {
+      expect(solveA(input), equals(421));
+    });
+  });
+  group('Part Two', () {
+    test('Example 1', () {
+      expect(
+          solveB(r'''
+7 6 4 2 1
+1 2 7 8 9
+9 7 6 2 1
+1 3 2 4 5
+8 6 4 4 1
+1 3 6 7 9
+'''
+              .asLines),
+          equals(4));
+    });
+    test('Solution', () {
+      expect(solveB(input), equals(476));
+    });
+  });
+}