Implement selection sort and in-place merge sort for RandomAccessFileList

src/main/java/com/moparisthebest/filelist/Main.java

@@ -1,6 +1,7 @@
 package com.moparisthebest.filelist;
 
 import java.io.IOException;
+import java.util.Comparator;
 import java.util.Date;
 import java.util.List;
 
@@ -11,7 +12,7 @@ public class Main {
     public static void main(String[] args) throws IOException {
         System.out.println("str " + new Date());
         //final List<Long> list = new RandomAccessFileList<>("/home/mopar/raf2.list", new UnsignedLongConverter(5));
-        final List<Long> list = new RandomAccessFileList<>("/home/mopar/raf2.list", LongConverter40Bit.instance);
+        final List<Long> list = new RandomAccessFileList<>("/home/mopar/raf2.list", LongConverter40Bit.instance); list.clear();
         /*
         System.out.println(list.get(0));
         System.out.println(((RandomAccessFileList)list).longSize());
@@ -35,14 +36,18 @@ public class Main {
         list.add(99999999999L);
         System.out.println(list.get(1));
         list.add(6L);
+        list.add(4L);
         System.out.println(list);
-        for(long l : list)
-            System.out.println(l);
         list.sort(Long::compareTo);
         System.out.println(list);
+        System.out.println("------");
+        //if(true) return;
         for(long l = 0; l < 1000; ++l)
+        //for(long l = 7; l < 11; ++l)
             list.add(l);
+        System.out.println(list);
         list.sort(Long::compareTo);
+        list.sort(Comparator.reverseOrder());
         System.out.println(list);
     }
 }

src/main/java/com/moparisthebest/filelist/RandomAccessFileList.java

@@ -4,8 +4,7 @@ import java.io.File;
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.RandomAccessFile;
-import java.util.AbstractList;
+import java.util.*;
-import java.util.Objects;
 
 /**
  * Created by mopar on 2/9/17.
@@ -19,7 +18,7 @@ public class RandomAccessFileList<T> extends AbstractList<T> {
     public RandomAccessFileList(final RandomAccessFile raf, final ByteArrayConverter<T> bac) {
         Objects.requireNonNull(raf);
         Objects.requireNonNull(bac);
-        if(bac.numBytes() < 1)
+        if (bac.numBytes() < 1)
             throw new IllegalArgumentException("bytesPerEntry must be > 0");
         this.raf = raf;
         this.buffer = new byte[bac.numBytes()];
@@ -44,7 +43,7 @@ public class RandomAccessFileList<T> extends AbstractList<T> {
 
     public T get(final long index) throws IOException {
         raf.seek(index * buffer.length);
-        if(raf.read(buffer) != buffer.length)
+        if (raf.read(buffer) != buffer.length)
             throw new IOException("no full buffer to read, corrupted file?");
         return bac.fromBytes(buffer);
     }
@@ -76,7 +75,7 @@ public class RandomAccessFileList<T> extends AbstractList<T> {
     @Override
     public T set(final int index, final T o) {
         try {
-            return this.set((long)index, o);
+            return this.set((long) index, o);
         } catch (IOException e) {
             throw new RuntimeException(e);
         }
@@ -98,4 +97,132 @@ public class RandomAccessFileList<T> extends AbstractList<T> {
             throw new RuntimeException(e);
         }
     }
+
+    @Override
+    public void sort(final Comparator<? super T> c) {
+        try {
+            //this.selectionSort(c);
+            this.inPlaceMergeSort(c);
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    public void selectionSort(final Comparator<? super T> c) throws IOException {
+        // a[0] to a[n-1] is the array to sort
+        final long n = this.longSize(), n1 = n - 1;
+        final byte[] tmp = new byte[this.buffer.length];
+
+        // advance the position through the entire array
+        //   (could do j < n-1 because single element is also min element)
+        for (long j = 0; j < n1; ++j) {
+            /* find the min element in the unsorted a[j .. n-1] */
+
+            /* assume the min is the first element */
+            long iMin = j;
+            /* test against elements after j to find the smallest */
+            for (long i = j + 1; i < n; ++i) {
+                // if this element is less, then it is the new minimum
+                // this order is important, we want get(iMin) done last so it's already in buffer below if we need to swap!
+                // in all cases except when iMin is last, in which case we have to seek back and read it, this is less common though usually
+                final T iObj = this.get(i);
+                if (c.compare(iObj, this.get(iMin)) <= 0){
+                    // found new minimum; remember its index
+                    iMin = i;
+                }
+            }
+
+            if (iMin != j) {
+                //swap(a[j], a[iMin]);
+
+                // buffer already has iMin value in it unless iMin was last value
+                if (iMin == n1) {
+                    // grab iMin to buffer
+                    raf.seek(iMin * buffer.length);
+                    if (raf.read(buffer) != buffer.length)
+                        throw new IOException("no full buffer to read, corrupted file?");
+                }
+
+                // grab j to tmp
+                raf.seek(j * buffer.length);
+                if (raf.read(tmp) != buffer.length)
+                    throw new IOException("no full buffer to read, corrupted file?");
+
+                //System.out.printf("iMin: %d j: %d buffer: %d tmp: %d%n", iMin, j, bac.fromBytes(buffer), bac.fromBytes(tmp));
+
+                // write buffer to j
+                raf.seek(j * buffer.length);
+                raf.write(buffer);
+
+                // write tmp to iMin
+                raf.seek(iMin * buffer.length);
+                raf.write(tmp);
+            }
+        }
+    }
+
+    /**
+     * In-Place Merge Sort.
+     * <p>
+     * Building on the algorithm core found in
+     * http://www.cs.ubc.ca/~harrison/Java/MergeSortAlgorithm.java.html
+     * http://penguin.ewu.edu/cscd300/Topic/AdvSorting/MergeSorts/InPlace.html
+     * http://penguin.ewu.edu/cscd300/Topic/AdvSorting/MergeSorts/MergeSort.java
+     */
+    public void inPlaceMergeSort(final Comparator<? super T> c) throws IOException {
+        this.inPlaceMergeSort(c, 0, this.longSize() - 1);
+    }
+
+    public void inPlaceMergeSort(final Comparator<? super T> c, final long first, final long last) throws IOException {
+        long mid, lt, rt;
+
+        if (first >= last) return;
+
+        mid = (first + last) / 2;
+
+        inPlaceMergeSort(c, first, mid);
+        inPlaceMergeSort(c, mid + 1, last);
+
+        lt = first;
+        rt = mid + 1;
+        // One extra check:  can we SKIP the merge?
+        if (c.compare(this.get(mid), this.get(rt)) <= 0)
+            return;
+
+        byte[] tmp = new byte[buffer.length], tmp2 = new byte[buffer.length], tmp3;
+
+        while (lt <= mid && rt <= last) {
+            // Select from left:  no change, just advance lt
+            if (c.compare(this.get(lt), this.get(rt)) <= 0)
+                ++lt;
+                // Select from right:  rotate [lt..rt] and correct
+            else {
+                // buffer contains rt here due to this.get(rt) being called last above, will move to [lt]
+
+                // scoot everything else over one todo: can do this in bigger chunks than buffer.length to speed things up...
+                //System.out.printf("lt: %d, rt: %d, rt-lt: %d, buffer: %d%n", lt, rt, rt-lt, bac.fromBytes(buffer));
+                raf.seek(lt * buffer.length);
+                raf.read(tmp);
+                for(long dst = lt + 1; dst <= lt + (rt - lt); ++dst){
+                    //raf.seek(dst * buffer.length);
+                    raf.read(tmp2);
+                    raf.seek(dst * buffer.length);
+                    raf.write(tmp);
+                    tmp3 = tmp2;
+                    tmp2 = tmp;
+                    tmp = tmp3;
+                }
+
+                // write buffer to lt
+                raf.seek(lt * buffer.length);
+                raf.write(buffer);
+
+                // EVERYTHING has moved up by one
+                lt++;
+                mid++;
+                rt++;
+            }
+        }
+        // Whatever remains in [rt..last] is in place
+    }
 }