day(07): add solution

Signed-off-by: Matej Focko <mfocko@redhat.com>

src/day07/Day07.kt

@@ -0,0 +1,29 @@
+package day07
+
+import readInputAsCommaSeparatedInts
+import kotlin.math.absoluteValue
+
+// for part 1, it's always included in the input set
+fun part1(input: List<Int>): Int = input.toSet().minOf { target ->
+    input.sumOf {
+        (it - target).absoluteValue
+    }
+}
+
+fun part2(input: List<Int>): Int = (input.minOrNull()!!..input.maxOrNull()!!).minOf { target ->
+    input.sumOf {
+        val diff = (it - target).absoluteValue
+        diff * (diff + 1) / 2
+    }
+}
+
+fun main() {
+    val testInput = readInputAsCommaSeparatedInts(7, "test_input").sorted()
+    val input = readInputAsCommaSeparatedInts(7, "input").sorted()
+
+    check(part1(testInput) == 37)
+    println(part1(input))
+
+    check(part2(testInput) == 168)
+    println(part2(input))
+}

src/day07/test_input.txt

@@ -0,0 +1 @@
+16,1,2,0,4,2,7,1,2,14