Day 2

2 files changed, 76 insertions, 0 deletions

diff --git a/Day 2/Day_02.swift b/Day 2/Day_02.swift
new file mode 100644
index 0000000..6d682bd
--- /dev/null
+++ b/Day 2/Day_02.swift
@@ -0,0 +1,75 @@
+#!/usr/bin/swift
+import Foundation
+
+guard CommandLine.arguments.count >= 2 else {
+  fatalError("Usage: ./Day_01 <input.txt>")
+}
+
+
+let ranges: [ClosedRange<Int>] = try! String.init(contentsOfFile: CommandLine.arguments[1],
+  encoding: .utf8)
+.split(separator: ",")
+.map { rangeString in
+  guard let separatorIdx = rangeString.firstIndex(of: "-"),
+  let lower = Int(rangeString[..<separatorIdx]),
+  let upper = Int(rangeString[rangeString.index(after: separatorIdx)...]) else {
+    fatalError("L16 : [ERROR] Failed to create ClosedRange!")
+  }
+  return lower...upper
+}
+
+var invalidIdSum: Int = 0
+
+for range in ranges {
+  for number in range {
+    let numString = String(number)
+    let length = numString.count
+    guard length.isMultiple(of: 2) else { continue }
+    let mid = numString.index(numString.startIndex, offsetBy: length / 2)
+    let left  = numString[numString.startIndex..<mid]
+    let right = numString[mid..<numString.endIndex]
+    if left == right {
+      invalidIdSum += number
+    }
+  }
+}
+print("=======Part 1=======\n\(invalidIdSum)")
+
+invalidIdSum = 0
+func isRepeating(_ x: Int) -> Bool {
+  if x == 0 { return false }
+  var digits = 0
+  var temp = x
+  while temp > 0 {
+    digits += 1
+    temp /= 10
+  }
+  if digits < 2 { return false }
+  for period in 1...(digits / 2) {
+    guard digits % period == 0 else { continue }
+    var divisor = 1
+    for _ in 0..<period {
+      divisor *= 10
+    }
+    let pattern = x % divisor
+    var reconstructed = 0
+    var multiplier = 1
+    for _ in 0..<(digits / period) {
+      reconstructed += pattern * multiplier
+      multiplier *= divisor
+    }
+    if reconstructed == x {
+      return true
+    }
+  }
+  return false
+}
+
+ranges.forEach { range in 
+  for id in range {
+    if isRepeating(id) {
+      invalidIdSum += id
+    }
+  }
+}
+print("=======Part 2=======\n\(invalidIdSum)")
\ No newline at end of file
diff --git a/Day 2/input.txt b/Day 2/input.txt
new file mode 100644
index 0000000..bfcd4e3
--- /dev/null
+++ b/Day 2/input.txt
@@ -0,0 +1 @@
+5959566378-5959623425,946263-1041590,7777713106-7777870316,35289387-35394603,400-605,9398763-9592164,74280544-74442206,85684682-85865536,90493-179243,202820-342465,872920-935940,76905692-76973065,822774704-822842541,642605-677786,3759067960-3759239836,1284-3164,755464-833196,52-128,3-14,30481-55388,844722790-844967944,83826709-83860070,9595933151-9595993435,4216-9667,529939-579900,1077949-1151438,394508-486310,794-1154,10159-17642,5471119-5683923,16-36,17797-29079,187-382
\ No newline at end of file