WIP power sort

app/src/main/java/de/uni_marburg/powersort/ASort.java

@@ -0,0 +1,129 @@
+package de.uni_marburg.powersort;
+
+import java.util.Comparator;
+import java.util.Stack;
+
+public class ASort {
+
+    private static class Run {
+        int start, end;
+        int power;
+
+        Run(int start, int end, int power) {
+            this.start = start;
+            this.end = end;
+            this.power = power;
+        }
+    }
+
+    public static <T> void sort(T[] array, Comparator<? super T> comparator) {
+        if (array == null || comparator == null) {
+            throw new IllegalArgumentException("Array and comparator must not be null");
+        }
+
+        int n = array.length;
+        if (n < 2) return;
+
+        Stack<Run> runs = new Stack<>();
+        int i = 0;
+
+        while (i < n) {
+            // Find the next run
+            int j = extendRunRight(array, comparator, i, n);
+
+            // Compute the power of the run
+            int power = calculatePower(runs.isEmpty() ? null : runs.peek(), i, j);
+
+            // Merge runs if needed based on power comparison
+            while (!runs.isEmpty() && power <= runs.peek().power) {
+                mergeRuns(array, comparator, runs);
+            }
+
+            // Push the current run
+            runs.push(new Run(i, j, power));
+            i = j;
+        }
+
+        // Merge remaining runs
+        while (runs.size() > 1) {
+            mergeRuns(array, comparator, runs);
+        }
+    }
+
+    private static <T> int extendRunRight(T[] array, Comparator<? super T> comparator, int start, int end) {
+        int runEnd = start + 1;
+
+        if (runEnd == end) return runEnd;
+
+        // Check for ascending or descending order
+        if (comparator.compare(array[runEnd], array[start]) < 0) {
+            // Descending run
+            while (runEnd < end && comparator.compare(array[runEnd], array[runEnd - 1]) < 0) {
+                runEnd++;
+            }
+            reverseRange(array, start, runEnd);
+        } else {
+            // Ascending run
+            while (runEnd < end && comparator.compare(array[runEnd], array[runEnd - 1]) >= 0) {
+                runEnd++;
+            }
+        }
+
+        return runEnd;
+    }
+
+    private static <T> void reverseRange(T[] array, int start, int end) {
+        end--;
+        while (start < end) {
+            T temp = array[start];
+            array[start++] = array[end];
+            array[end--] = temp;
+        }
+    }
+
+    private static int calculatePower(Run previousRun, int currentStart, int currentEnd) {
+        if (previousRun == null) {
+            return 0; // First run
+        }
+
+        int previousSize = previousRun.end - previousRun.start;
+        int currentSize = currentEnd - currentStart;
+        return (int) (Math.log(previousSize + currentSize) / Math.log(2));
+    }
+
+    private static <T> void mergeRuns(T[] array, Comparator<? super T> comparator, Stack<Run> runs) {
+        Run run2 = runs.pop();
+        Run run1 = runs.pop();
+
+        merge(array, comparator, run1.start, run1.end, run2.end);
+        runs.push(new Run(run1.start, run2.end, calculatePower(null, run1.start, run2.end)));
+    }
+
+    private static <T> void merge(T[] array, Comparator<? super T> comparator, int lo, int mid, int hi) {
+        T[] left = java.util.Arrays.copyOfRange(array, lo, mid);
+        int i = 0, j = mid, k = lo;
+
+        while (i < left.length && j < hi) {
+            if (comparator.compare(left[i], array[j]) <= 0) {
+                array[k++] = left[i++];
+            } else {
+                array[k++] = array[j++];
+            }
+        }
+
+        while (i < left.length) {
+            array[k++] = left[i++];
+        }
+    }
+
+    public static void main(String[] args) {
+        Integer[] array = {5, 2, 9, 1, 5, 6, 3, 7, 4, 8};
+        System.out.println("Before sorting:");
+        java.util.Arrays.stream(array).forEach(e -> System.out.print(e + " "));
+
+        sort(array, Integer::compareTo);
+
+        System.out.println("\nAfter sorting:");
+        java.util.Arrays.stream(array).forEach(e -> System.out.print(e + " "));
+    }
+}