day2 part1

Author: spaenleh

Sources/AdventOfCode.swift

@@ -2,7 +2,8 @@ import ArgumentParser
 
 // Add each new day implementation to this array:
 let allChallenges: [any AdventDay] = [
-  Day01()
+  Day01(),
+  Day02(),
 ]
 
 @main

Sources/Day02.swift

@@ -0,0 +1,75 @@
+import Algorithms
+
+struct Report {
+  var value: [Int]
+
+}
+extension Report {
+  init(_ data: Substring) {
+    value = data.split(separator: " ").map { v in Int(v) ?? 0 }
+  }
+}
+
+func spreadsWell(_ value: Int) -> Bool {
+  abs(value) <= 3 && abs(value) >= 1
+}
+
+struct ReportAnalyzer {
+
+  func isSafe(report: Report, damped: Bool = false) -> Bool {
+    // all values are either increasing or decreasing
+    let diffs = report.value.adjacentPairs().map { (one, two) in
+      two - one
+    }
+    let order = diffs.grouped { v in
+      if v < 0 {
+        return "desc"
+      }
+      if v > 0 {
+        return "asc"
+      }
+      return "none"
+    }
+    let spread = diffs.filter { spreadsWell($0) }
+
+    let isSafe = order.count == 1 && spread.count == diffs.count
+    if damped {
+
+      let orderIsOffByOne =
+        order.count == 2
+        && (order["desc", default: []].count == 1 || order["asc", default: []].count == 1)
+      // let spreadIsOffByOne = spread.count == diffs.count - 1
+      let spreadDefect = diffs.firstIndex { spreadsWell($0) == false }
+      if let defect = spreadDefect {
+        print(defect, report.value)
+        return ReportAnalyzer().isSafe(
+          report: Report(
+            value: report.value.filter {
+              $0 == report.value[defect + 1]
+            }))
+      }
+      // print("\(report): safe (\(isSafe)) order (\(orderIsOffByOne)) spread (\(spreadIsOffByOne))")
+      return isSafe || orderIsOffByOne
+    }
+
+    return isSafe
+  }
+}
+
+struct Day02: AdventDay {
+  // Save your data in a corresponding text file in the `Data` directory.
+  var data: String
+
+  var reports: [Report] {
+    data.split(separator: "\n").map { Report($0) }
+  }
+
+  func part1() -> Int {
+    reports.map { ReportAnalyzer().isSafe(report: $0) }.filter { $0 }.count
+  }
+
+  func part2() -> Int {
+    reports.map { ReportAnalyzer().isSafe(report: $0, damped: true) }.filter { $0 }.count
+
+  }
+}

Tests/Day02.swift

@@ -0,0 +1,33 @@
+import Testing
+
+@testable import aoc
+
+@Suite("Day02")
+struct Day02Tests {
+  let testData = """
+    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
+    """
+
+  @Test("report analyzer")
+  func name() async throws {
+    #expect(Report("7 6 4 2 1").value == [7, 6, 4, 2, 1])
+    #expect(ReportAnalyzer().isSafe(report: Report("7 6 4 2 1")) == true)
+  }
+
+  @Test("part1")
+  func testPart1() async throws {
+    let challenge = Day02(data: testData)
+    #expect(challenge.part1() == 2)
+  }
+
+  @Test("part2")
+  func testPart2() async throws {
+    let challenge = Day02(data: testData)
+    #expect(challenge.part2() == 4)
+  }
+}