Add quick sort code

jbee37142 · jbee37142 · commit 650a9aa2223d · 2017-06-04T19:11:42.000+09:00
diff --git a/src/test/java/sort/QuickSort.java b/src/test/java/sort/QuickSort.java
@@ -0,0 +1,57 @@
+package sort;
+
+import org.junit.Test;
+import utils.Utils;
+
+import static org.hamcrest.CoreMatchers.is;
+import static org.junit.Assert.assertThat;
+
+public class QuickSort {
+
+    /*
+        TASK
+        Quick sort를 구현한다.
+     */
+
+    @Test
+    public void test() {
+        int[] arr1 = {};
+        int[] sortedArr1 = {};
+        assertThat(solution(arr1, 0, arr1.length - 1), is(sortedArr1));
+        int[] arr2 = {6,4,1,8,9,2,7,5,3};
+        int[] sortedArr2 = {1,2,3,4,5,6,7,8,9};
+        assertThat(solution(arr2, 0, arr2.length - 1), is(sortedArr2));
+        int[] arr3 = {1};
+        int[] sortedArr3 = {1};
+        assertThat(solution(arr3, 0, arr3.length - 1), is(sortedArr3));
+    }
+
+    public int[] solution(int[] arr, int left, int right) {
+        if (arr == null) return null;
+
+        int[] result = arr;
+        if (left >= right) return result;
+
+        int pivotPos = partition(result, left, right);
+
+        result = solution(result, left, pivotPos - 1);
+        result = solution(result, pivotPos + 1, right);
+
+        return result;
+    }
+
+    private int partition(int[] arr, int left, int right) {
+        if (arr == null || left < 0) return -1;
+        int pivotValue = arr[right];
+        int endOfLowBlock = left - 1;
+
+        for (int pos = left; pos < right; pos++) {
+            if (pivotValue > arr[pos]) {
+                Utils.swapValue(arr, pos, ++endOfLowBlock);
+            }
+        }
+        Utils.swapValue(arr, right, ++endOfLowBlock);
+
+        return endOfLowBlock;
+    }
+}
