improved (a lot) day 5 puzzle 2

src/day5/Puzzle2.scala

@@ -14,10 +14,15 @@ object Puzzle2 {
     def backward(dst: Long): Long = startSrc + dst - startDst
     override def toString: String = s"[$startSrc;$endSrc[ -> ($dstTable) [$startDst;$endDst["
   }
+
   class Table(val id: Int) {
     var ranges: ArrayBuffer[Range] = new ArrayBuffer()
 
     def addRange(range: Range): Unit = ranges.addOne(range)
+
+    /**
+     * Sorts the ranges in ascending order
+     */
     def sortRanges(): Unit = {
       var changed: Boolean = false
       do {
@@ -33,6 +38,9 @@ object Puzzle2 {
       } while (changed)
     }
 
+    /**
+     * Fills the gaps between ranges with identity ranges (i.e. which keep values unchanged)
+     */
     def fillGaps(): Unit = {
       var r1: Range = Range(0, 0, 0, id + 1)
       var r2: Range = r1
@@ -49,12 +57,23 @@ object Puzzle2 {
       }
     }
 
+    /**
+     * Forwards a value through this table
+     * @param src The source to forward
+     * @return A pair containing the destination value and new table id
+     */
     def forward(src: Long): (Long, Int) = {
       for (range: Range <- ranges) {
         if (range.containsSrc(src)) return (range.forward(src), range.dstTable)
       }
       return (src, id+1)
     }
+
+    /**
+     * Forwards a value in reverse through this table
+     * @param dst The destination to "backward"
+     * @return A pair containing the source value and new table id
+     */
     def backward(dst: Long): (Long, Int) = {
       for (range: Range <- ranges) {
         if (range.containsDst(dst)) return (range.backward(dst), id)
@@ -67,6 +86,7 @@ object Puzzle2 {
 
   var forwardingTables: Array[Table] = Array.empty
   var seeds: Array[Long] = Array.empty
+
   def loadInput(path: String): Unit = {
     val source: BufferedSource = Source.fromFile(path)
 
@@ -89,6 +109,9 @@ object Puzzle2 {
     source.close()
   }
 
+  /**
+   * Reorganizes all the tables by sorting the ranges and filling the gaps between them
+   */
   def sortTables(): Unit = {
     for (table: Table <- forwardingTables) {
       table.sortRanges()
@@ -96,50 +119,24 @@ object Puzzle2 {
     }
   }
 
-  def simplifyTables(): Unit = {
+  /**
+   * Collapses all forwarding tables into a single one, mapping seeds to locations
+   */
+  def collapseTables(): Unit = {
     for (i: Int <- forwardingTables.length - 1 until 0 by -1) {
-      //simplifyTable(i)
-      val newTable: Table = collapseTables(forwardingTables(i-1), forwardingTables(i))
+      val newTable: Table = collapseTable(forwardingTables(i-1), forwardingTables(i))
       forwardingTables(i-1) = newTable
     }
   }
 
-  def simplifyTable(tableI: Int): Unit = {
-    val table1: Table = forwardingTables(tableI)
-    val table2: Table = forwardingTables(tableI+1)
-
-    val newTable1: Table = new Table(table1.id)
-    val limits: ArrayBuffer[Long] = new ArrayBuffer()
-
-    for (r1: Range <- table1.ranges) {
-      val startFrom1 = r1.startSrc
-      val endFrom1 = startFrom1 + r1.length
-      val startTo1 = r1.startDst
-      val endTo1 = startTo1 + r1.length
-
-      limits.addOne(startTo1)
-      limits.addOne(endTo1)
-
-      for (r2: Range <- table2.ranges) {
-        val startFrom2 = r2.startSrc
-        val endFrom2 = startFrom2 + r2.length
-        val startTo2 = r2.startDst
-        val endTo2 = startTo2 + r2.length
-
-        limits.addOne(startFrom2)
-        limits.addOne(endFrom2)
-
-        // If overlap
-        if (!(endTo1 < startFrom2 || startTo1 > endFrom2)) {
-          
-        }
-      }
-    }
-
-    forwardingTables(tableI) = newTable1
-  }
-
-  def collapseTables(table1: Table, table2: Table): Table = {
+  /**
+   * Collapses a forwarding table with the next tables
+   * @param table1 The table to collapse
+   * @param table2 The next table
+   * @return A new table equivalent to the fusion of both tables
+   */
+  def collapseTable(table1: Table, table2: Table): Table = {
+    // Find all new range limits
     val limitsSet: mutable.Set[Long] = new mutable.HashSet()
     limitsSet.addOne(table1.ranges(0).startSrc)
     for (range: Range <- table1.ranges) {
@@ -152,6 +149,8 @@ object Puzzle2 {
 
     val newTable: Table = new Table(table1.id)
     val limits: Array[Long] = limitsSet.toArray.sorted
+
+    // For each limit, create the corresponding range by forwarding table 1 through table 2
     for (i: Int <- 0 until limits.length - 1) {
       val src1: Long = limits(i)
       val dst1: (Long, Int) = table1.forward(src1)
@@ -162,42 +161,40 @@ object Puzzle2 {
     return newTable
   }
 
-  def forward(value: Long, tableI: Int): Long = {
-    for (range: Range <- forwardingTables(tableI).ranges) {
-      if (value >= range.startSrc) {
-        if (value < range.startSrc + range.length) {
-          return value - range.startSrc + range.startDst
-        }
-      } else {
-        return value
-      }
-    }
-    return value
-  }
   def solve(path: String): Long = {
     println("Solving puzzle 2")
     loadInput(path)
     println("Loaded input")
     sortTables()
-    for (table: Table <- forwardingTables) {
+    /*for (table: Table <- forwardingTables) {
       println(table)
-    }
+    }*/
     println("Sorted forwarding tables")
-    simplifyTables()
+    collapseTables()
     println("Simplified forwarding tables")
     val table: Table = forwardingTables(0)
-    println(table)
+    //println(table)
 
     var smallest: Long = -1
     for (i: Int <- seeds.indices by 2) {
-      println(s"Mapping range of seed [${seeds(i)},${seeds(i)+seeds(i+1)}]")
-      for (seed: Long <- seeds(i) until seeds(i)+seeds(i+1)) {
-        val location: Long = table.forward(seed)._1
-        if (smallest == -1 || location < smallest) {
-          smallest = location
-        }
+      val seedStart: Long = seeds(i)
+      val seedEnd: Long = seedStart + seeds(i+1) - 1
+
+      // Find range limits lying inside seed range
+      val limitsSet: mutable.Set[Long] = new mutable.HashSet()
+      limitsSet.addOne(seedStart)
+      limitsSet.addOne(seedEnd)
+      for (r2: Range <- table.ranges) {
+        if (r2.startSrc > seedStart && r2.startSrc < seedEnd) limitsSet.add(r2.startSrc)
+        if (r2.endSrc > seedStart && r2.endSrc < seedEnd) limitsSet.add(r2.startSrc)
+      }
+      val limits: Array[Long] = limitsSet.toArray.sorted
+
+      // For each limit, forward its value and compare with current smallest
+      for (i: Int <- 0 until limits.length - 1) {
+        val value: Long = table.forward(limits(i))._1
+        if (smallest == -1 || value < smallest) smallest = value
       }
-      println(s"New smallest location: $smallest")
     }
     return smallest
   }