Inverse number

Author: ProgrammingLanguageLeader

src/algorithms/inverse_number/Main.java

@@ -0,0 +1,64 @@
+package algorithms.inverse_number;
+
+import java.util.Scanner;
+
+public class Main {
+    private long inverseNumber;
+
+    public Main() {
+        inverseNumber = 0;
+    }
+
+    private void run() {
+        Scanner scanner = new Scanner(System.in);
+        int arraySize = scanner.nextInt();
+        int[] array = new int[arraySize];
+        for (int i = 0; i < arraySize; i++) {
+            array[i] = scanner.nextInt();
+        }
+        int[] sortedArray = mergeSort(array, 0, array.length);
+        System.out.println(inverseNumber);
+    }
+
+    private int[] mergeSort(int[] array, int from, int to) {
+        if (to - from == 1) {
+            int[] oneElementArray = new int[1];
+            oneElementArray[0] = array[from];
+            return oneElementArray;
+        }
+        int midPoint = (from + to) / 2;
+        return merge(
+                mergeSort(array, from, midPoint),
+                mergeSort(array, midPoint, to)
+        );
+    }
+
+    private int[] merge(int[] leftArray, int[] rightArray) {
+        int leftIndex = 0, rightIndex = 0;
+        int[] merged = new int[leftArray.length + rightArray.length];
+        for (int i = 0; i < leftArray.length + rightArray.length; i++) {
+            if (leftIndex < leftArray.length && rightIndex < rightArray.length) {
+                if (leftArray[leftIndex] > rightArray[rightIndex]) {
+                    merged[i] = rightArray[rightIndex++];
+                    inverseNumber += leftArray.length - leftIndex;
+                }
+                else {
+                    merged[i] = leftArray[leftIndex++];
+                }
+            }
+            else {
+                if (rightIndex < rightArray.length) {
+                    merged[i] = rightArray[rightIndex++];
+                }
+                else {
+                    merged[i] = leftArray[leftIndex++];
+                }
+            }
+        }
+        return merged;
+    }
+
+    public static void main(String[] args) {
+        new Main().run();
+    }
+}