09: part2 is wrong :(

Author: jamOne-

.idea/workspace.xml

@@ -0,0 +1,105 @@
+import java.math.BigInteger
+
+fun main() {
+    println(solve09a(readInputLines("09")))
+    println(solve09b(readInputLines("09")))
+}
+
+fun solve09a(lines: List<String>): BigInteger = checksum(fragmentBlocks(readInput(lines[0])))
+
+fun solve09b(lines: List<String>): BigInteger = checksum(fragmentBlocks2(readInput(lines[0])))
+
+private data class Block(val id: Int, val size: Int, val freeAfter: Int, val moved: Boolean = false)
+
+private fun readInput(disk: String): List<Block> {
+    val fixedDisk = if (disk.length % 2 != 0) disk + '0' else disk
+    val result = mutableListOf<Block>()
+    var id = 0
+
+    for (s in fixedDisk.windowed(2, 2)) {
+        val size = s[0].digitToInt()
+        val free = s[1].digitToInt()
+        result.add(Block(id, size, free))
+        id += 1
+    }
+
+    return result
+}
+
+private fun fragmentBlocks(blocks: List<Block>): List<Block> {
+    val bs = blocks.toMutableList()
+    val result = mutableListOf(Block(blocks[0].id, blocks[0].size, 0))
+
+    var i = 0
+    var j = bs.lastIndex
+
+    while (i < j) {
+        if (bs[i].freeAfter > bs[j].size) {
+            result.add(bs[j].copy(freeAfter = 0))
+            bs[i] = bs[i].copy(freeAfter = bs[i].freeAfter - bs[j].size)
+            j -= 1
+        } else if (bs[i].freeAfter < bs[j].size) {
+            result.add(Block(bs[j].id, bs[i].freeAfter, 0))
+            bs[j] = bs[j].copy(size = bs[j].size - bs[i].freeAfter)
+            i += 1
+            result.add(bs[i].copy(freeAfter = 0))
+        } else {
+            result.add(bs[j].copy(freeAfter = 0))
+            i += 1
+            j -= 1
+            if (i != j + 1) {
+                result.add(bs[i].copy(freeAfter = 0))
+            }
+        }
+    }
+
+
+    return result
+}
+
+private fun fragmentBlocks2(blocks: List<Block>): List<Block> {
+    val result = blocks.toMutableList()
+
+    var i = blocks.lastIndex
+    while (i > 0) {
+        val ib = result[i]
+        if (ib.moved) {
+            i -= 1
+            continue
+        }
+
+        var moved = false
+        for (j in 0 until i) {
+            val jb = result[j]
+            if (jb.freeAfter >= ib.size) {
+                result[i - 1] = result[i - 1].copy(freeAfter = result[i - 1].freeAfter + ib.freeAfter + ib.size)
+                result.removeAt(i)
+                result[j] = jb.copy(freeAfter = 0)
+                result.add(j + 1, ib.copy(freeAfter = jb.freeAfter - ib.size, moved = true))
+                moved = true
+                break
+            }
+        }
+        if (!moved) {
+            i -= 1
+        }
+    }
+
+
+    return result
+}
+
+private fun checksum(blocks: List<Block>): BigInteger {
+    var total = BigInteger.ZERO
+    var i = 0
+
+    for (block in blocks) {
+        for (j in 0 until block.size) {
+            total += block.id.toBigInteger() * i.toBigInteger()
+            i += 1
+        }
+        i += block.freeAfter
+    }
+
+    return total
+}