Advent of Code 2020 in Kotlin

Author: flwyd

2020/.gitignore

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+classes/
+output.*.txt

2020/dec1/Makefile

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+# Copyright 2021 Google LLC
+#
+# Use of this source code is governed by an MIT-style
+# license that can be found in the LICENSE file or at
+# https://opensource.org/licenses/MIT.
+
+# https://adventofcode.com/2020/day/1
+
+KOTLIN = kotlin
+KOTLINC = kotlinc
+CLASSES = classes
+PACKAGE = dec1
+MAIN_CLASS = Dec1Kt
+
+compile: $(CLASSES)/$(PACKAGE)/$(MAIN_CLASS).class
+
+$(CLASSES)/$(PACKAGE)/$(MAIN_CLASS).class: $(PACKAGE).kt
+	@mkdir -p $(CLASSES)
+	$(KOTLINC) -d $(CLASSES) $(PACKAGE).kt
+
+output.%.txt: input.%.txt compile
+	$(KOTLIN) -cp $(CLASSES) $(PACKAGE).$(MAIN_CLASS) < $< | tee $@
+
+out: output.example.txt output.actual.txt
+
+clean:
+	rm -r $(CLASSES)

2020/dec1/dec1.kt

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+/*
+ * Copyright 2021 Google LLC
+ *
+ * Use of this source code is governed by an MIT-style
+ * license that can be found in the LICENSE file or at
+ * https://opensource.org/licenses/MIT.
+ */
+
+package dec1
+
+import kotlin.time.ExperimentalTime
+import kotlin.time.TimeSource
+import kotlin.time.measureTimedValue
+
+/* Input is integers. Find the two which sum to 2020, print their product. */
+object Part1 {
+  fun solve(lines: Sequence<String>): String {
+    val seen = mutableSetOf<Int>()
+    return lines.map(String::toInt)
+      .filter {
+        try {
+          (2020 - it) in seen
+        } finally {
+          seen.add(it)
+        }
+      }
+      // .map { it.also(seen::add) } // would incorrectly match 1010 with itself
+      // .filter { (2020 - it) in seen }
+      .map { it * (2020 - it) }
+      .joinToString("\n")
+  }
+}
+
+/* Input is integers. Find three which sum to 2020, print their product. */
+object Part2 {
+  fun solve(lines: Sequence<String>): String {
+    val seen = mutableSetOf<Int>()
+    val sums = mutableMapOf<Int, Pair<Int, Int>>()
+    val results = mutableListOf<Int>()
+    for (i in lines.map(String::toInt)) {
+      if ((2020 - i) in sums) {
+        results.add(sums.getValue(2020 - i).let { i * it.first * it.second })
+      }
+      seen.forEach { x: Int -> sums[x + i] = x to i }
+      seen.add(i)
+    }
+    return results.joinToString("\n")
+  }
+}
+
+@ExperimentalTime
+@Suppress("UNUSED_PARAMETER")
+fun main(args: Array<String>) {
+  val lines = generateSequence(::readLine).toList()
+  println("Part 1:")
+  TimeSource.Monotonic.measureTimedValue { Part1.solve(lines.asSequence()) }.let {
+    println(it.value)
+    println("Completed in ${it.duration}")
+  }
+  println("Part 2:")
+  TimeSource.Monotonic.measureTimedValue { Part2.solve(lines.asSequence()) }.let {
+    println(it.value)
+    println("Completed in ${it.duration}")
+  }
+}

2020/dec1/input.actual.txt

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+1429
+1368
+1661
+1687
+1593
+1495
+1565
+1500
+1635
+1845
+1645
+1999
+1415
+1054
+1930
+1774
+1405
+1993
+1757
+1623
+1675
+1665
+631
+1950
+1702
+1311
+1509
+1790
+1643
+1884
+226
+1455
+1679
+1746
+1284
+1342
+1684
+1543
+1396
+1806
+1523
+1363
+1011
+1577
+1767
+1287
+1885
+1517
+1556
+1722
+1260
+1624
+1466
+1263
+1162
+1688
+1202
+1913
+1964
+1385
+1970
+1976
+1431
+858
+1748
+1544
+1438
+1300
+1926
+1587
+1376
+1939
+1039
+1639
+1539
+1491
+1631
+1521
+1564
+1507
+1637
+1534
+1713
+1533
+1118
+1356
+2003
+282
+1079
+1837
+1259
+1941
+1836
+1903
+1433
+1467
+1027
+1441
+1048
+1742
+1087
+1872
+1476
+1657
+1361
+1182
+1494
+1529
+1822
+1444
+1330
+1514
+1723
+1432
+1683
+1997
+1443
+1474
+1932
+1504
+1313
+1765
+19
+1784
+1619
+992
+1560
+1680
+1626
+1558
+1899
+1293
+1676
+1161
+1140
+1341
+1597
+1628
+1611
+1302
+1269
+1241
+1952
+1591
+1726
+428
+1703
+1289
+1109
+1478
+1002
+1817
+1849
+1838
+1319
+1641
+583
+1920
+1453
+1411
+1870
+1763
+1469
+1646
+1719
+1213
+1462
+1545
+1682
+1711
+18
+2004
+1252
+1620
+1559
+1315
+781
+1656
+1987
+1436
+1630
+1985
+1897
+1551
+1296
+1282
+1735
+1320
+1659
+1271
+1380
+1274
+1876
+1492
+1298
+1399
+1692
+1265
+1555
+1337

2020/dec1/input.example.txt

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+1721
+979
+366
+299
+675
+1456

2020/dec10/Makefile

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+# Copyright 2021 Google LLC
+#
+# Use of this source code is governed by an MIT-style
+# license that can be found in the LICENSE file or at
+# https://opensource.org/licenses/MIT.
+
+# https://adventofcode.com/2020/day/10
+
+KOTLIN = kotlin
+KOTLINC = kotlinc
+CLASSES = classes
+PACKAGE = dec10
+MAIN_CLASS = Dec10Kt
+
+compile: $(CLASSES)/$(PACKAGE)/$(MAIN_CLASS).class
+
+$(CLASSES)/$(PACKAGE)/$(MAIN_CLASS).class: $(PACKAGE).kt
+	@mkdir -p $(CLASSES)
+	$(KOTLINC) -d $(CLASSES) $(PACKAGE).kt
+
+output.%.txt: input.%.txt compile
+	$(KOTLIN) -cp $(CLASSES) $(PACKAGE).$(MAIN_CLASS) < $< | tee $@
+
+out: output.example.txt output.example2.txt output.actual.txt
+
+clean:
+	rm -r $(CLASSES)