Java快速排序的遞歸與非遞歸實現

Java中快速排序算法的遞歸和非遞歸實現都是常見的排序方法。下面分別給出兩種實現方式的代碼示例：

1. 遞歸實現：

public class QuickSortRecursive {
    public static void main(String[] args) {
        int[] arr = {10, 7, 8, 9, 1, 5};
        quickSort(arr, 0, arr.length - 1);
        System.out.println(Arrays.toString(arr));
    }

    public static void quickSort(int[] arr, int low, int high) {
        if (low< high) {
            int pivotIndex = partition(arr, low, high);
            quickSort(arr, low, pivotIndex - 1);
            quickSort(arr, pivotIndex + 1, high);
        }
    }

    public static int partition(int[] arr, int low, int high) {
        int pivot = arr[high];
        int i = low - 1;
        for (int j = low; j< high; j++) {
            if (arr[j] <= pivot) {
                i++;
                swap(arr, i, j);
            }
        }
        swap(arr, i + 1, high);
        return i + 1;
    }

    public static void swap(int[] arr, int i, int j) {
        int temp = arr[i];
        arr[i] = arr[j];
        arr[j] = temp;
    }
}

2. 非遞歸實現：

import java.util.Arrays;
import java.util.Stack;

public class QuickSortNonRecursive {
    public static void main(String[] args) {
        int[] arr = {10, 7, 8, 9, 1, 5};
        quickSort(arr);
        System.out.println(Arrays.toString(arr));
    }

    public static void quickSort(int[] arr) {
        Stack<Integer> stack = new Stack<>();
        stack.push(0);
        stack.push(arr.length - 1);

        while (!stack.isEmpty()) {
            int high = stack.pop();
            int low = stack.pop();

            if (low< high) {
                int pivotIndex = partition(arr, low, high);
                stack.push(low);
                stack.push(pivotIndex - 1);
                stack.push(pivotIndex + 1);
                stack.push(high);
            }
        }
    }

    public static int partition(int[] arr, int low, int high) {
        int pivot = arr[high];
        int i = low - 1;
        for (int j = low; j< high; j++) {
            if (arr[j] <= pivot) {
                i++;
                swap(arr, i, j);
            }
        }
        swap(arr, i + 1, high);
        return i + 1;
    }

    public static void swap(int[] arr, int i, int j) {
        int temp = arr[i];
        arr[i] = arr[j];
        arr[j] = temp;
    }
}

這兩個示例中，遞歸實現使用了函數調用棧來存儲待處理的子數組的邊界，而非遞歸實現使用了一個顯式的棧來達到相同的目的。在實際應用中，選擇哪種實現方式取決于特定問題和需求。