Quick Sort in Java

Sorting Algorithms/quick_sort.java

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+public class QuickSort {
+
+    private static int compare(int[] arr, int i, int j) {
+        if (arr[i] > arr[j]) {
+            return i;
+        } else {
+            return j;
+        }
+    }
+
+    /*
+    This method returns the index of median of array at i, j, k.
+    @param arr: Input array to be sorted.
+    @param i: Left end index of array.
+    @param j: Right end index of array.
+    @param k: Middle index of array.
+    @return: Index of median of array at i, j, k.
+    */
+    private static int median(int[] arr, int i, int j, int k) {
+        if (arr[i] > arr[j] && arr[i] > arr[k]) {
+            return compare(arr, k, j);
+        } else if (arr[j] > arr[i] && arr[j] > arr[k]) {
+            return compare(arr, k, i);
+        } else {
+            return compare(arr, i, j);
+        }
+    }
+
+    private static int partition(int[] arr, int start, int end) {
+        int l = median(arr, start, end, (start + end) / 2);
+        int p_idx = start - 1;
+        int tmp = arr[l];
+        arr[l] = arr[end];
+        arr[end] = tmp;
+        int pivot = arr[end];
+        for (int i = start; i < end; ++i) {
+            if (arr[i] <= pivot) {
+                p_idx++;
+                tmp = arr[i];
+                arr[i] = arr[p_idx];
+                arr[p_idx] = tmp;
+            }
+        }
+        p_idx++;
+        tmp = arr[p_idx];
+        arr[p_idx] = arr[end];
+        arr[end] = tmp;
+        return p_idx;
+    }
+
+    public static void quickSort(int[] a, int left, int right) {
+        if (left < right) {
+            int pi = partition(a, left, right);  //pi index of pivot
+            quickSort(a, left, pi - 1);  //sort left of pivot
+            quickSort(a, pi + 1, right);  //sort right of pivot
+        }
+    }
+
+    public static void main(String[] args) {
+        int[] arr = new int[] {2, 4, 2, 6, 7, -1};
+        quickSort(arr, 0, arr.length - 1);
+        for (int element : arr) {
+            System.out.println(element);
+        }
+    }
+}