퀵 정렬 구현

Author: gunkim

algorithm/src/main/java/io/github/gunkim/algorithm/sorting/QuickSort.java

@@ -0,0 +1,67 @@
+package io.github.gunkim.algorithm.sorting;
+
+public class QuickSort implements Sort {
+    private static final int MINIMUM_ARRAY_SIZE = 2;
+
+    private final int[] numbers;
+    private boolean sorted = false;
+
+    public QuickSort(int[] numbers) {
+        validateInput(numbers);
+        this.numbers = numbers;
+    }
+
+    private void validateInput(int[] numbers) {
+        if (numbers == null) {
+            throw new IllegalArgumentException("Input array must not be null");
+        }
+        if (numbers.length < MINIMUM_ARRAY_SIZE) {
+            throw new IllegalArgumentException("Input array must have at least " + MINIMUM_ARRAY_SIZE + " elements");
+        }
+    }
+
+    @Override
+    public int[] sort() {
+        if (sorted) {
+            return numbers;
+        }
+        quickSort(0, numbers.length - 1);
+        sorted = true;
+        return numbers;
+    }
+
+    private void quickSort(int start, int end) {
+        if (start >= end) {
+            return;
+        }
+        int pivotIndex = partition(start, end);
+        quickSort(start, pivotIndex - 1);
+        quickSort(pivotIndex + 1, end);
+    }
+
+    private int partition(int start, int end) {
+        int pivot = numbers[start];
+        int leftPointer = start + 1;
+        int rightPointer = end;
+
+        while (leftPointer <= rightPointer) {
+            while (leftPointer <= end && pivot >= numbers[leftPointer]) {
+                leftPointer++;
+            }
+            while (rightPointer > start && pivot < numbers[rightPointer]) {
+                rightPointer--;
+            }
+            if (leftPointer < rightPointer) {
+                swap(leftPointer, rightPointer);
+            }
+        }
+        swap(start, rightPointer);
+        return rightPointer;
+    }
+
+    private void swap(int i, int j) {
+        int temp = numbers[i];
+        numbers[i] = numbers[j];
+        numbers[j] = temp;
+    }
+}

algorithm/src/main/java/io/github/gunkim/algorithm/sorting/Sort.java

@@ -0,0 +1,5 @@
+package io.github.gunkim.algorithm.sorting;
+
+public interface Sort {
+    int[] sort();
+}