fix quick sort partition for special inputs and update testcase (#52)

pedrovgs · Apr 14, 2019 · ed6f8a4 · ed6f8a4
1 parent 4e22141
commit ed6f8a4
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Showing 2 changed files with 17 additions and 12 deletions.
diff --git a/src/main/java/com/github/pedrovgs/problem80/QuickSort.java b/src/main/java/com/github/pedrovgs/problem80/QuickSort.java
@@ -57,19 +57,13 @@ private void quickSort(int[] numbers, int left, int right) {
 
   private int partition(int[] numbers, int left, int right) {
     int pivot = numbers[right];
-    while (left < right) {
-      while (numbers[left] < pivot) {
-        left++;
-      }
-      while (numbers[right] > pivot) {
-        right--;
-      }
-      if (left <= right) {
-        int temp = numbers[left];
-        numbers[left] = numbers[right];
-        numbers[right] = temp;
+    int i = left - 1;
+    for (int j = left; j < right; ++j) {
+      if (numbers[j] <= pivot) {
+        swap(numbers, ++i, j);
       }
     }
-    return left; //pivot index
+    swap(numbers, ++i, right);
+    return i;
   }
 }
diff --git a/src/test/java/com/github/pedrovgs/sortingalgorithms/SortingAlgorithmTest.java b/src/test/java/com/github/pedrovgs/sortingalgorithms/SortingAlgorithmTest.java
@@ -79,4 +79,15 @@ public abstract class SortingAlgorithmTest {
     int[] expectedArray = { 1, 2, 3, 4 };
     assertArrayEquals(expectedArray, input);
   }
+
+  @Test(timeout = 5 * 1000)
+  public void shouldSortSpecialArray() {
+    int[] input = {12, -37, -5, 43, 62, 45, -95, -70, -55, -62, -24, -14,
+            -75, 43, 9, 58, -62, -22, -55};
+
+    sortingAlgorithm.sort(input);
+
+    int[] expectedArray = {-95, -75, -70, -62, -62, -55, -55, -37, -24, -22, -14, -5, 9, 12, 43, 43, 45, 58, 62};
+    assertArrayEquals(expectedArray, input);
+  }
 }