快速排序简单实现

public class QuickSort {

    public static int partition(int[] arr, int low, int high){
        if (arr == null || low >= arr.length || low < 0 || high >= arr.length || high < 0){
            return -1;//错误入参
        }
        int pivotPos = low;
        int pivot = arr[low];
        while(low < high){
            while (low < high && arr[high] >= pivot){
                high--;
            }
            while (low < high && arr[low] <= pivot){
                low++;
            }
            if (low < high) {
                swap(arr, low, high);
            }
        }
        swap(arr, pivotPos, low);
        return low;
    }


    public static void swap(int arr[], int a, int b){
        if (a >= arr.length || a < 0 || b >= arr.length || b < 0){
            return;
        }

        int temp = arr[a];
        arr[a] = arr[b];
        arr[b] = temp;
    }

    public static void quickSort(int[] arr, int low, int high){
    //递归实现
         if (arr == null || low < 0 || high <= 0 || low>high)
                return;
         int k = partition(arr, low, high);
        if (k < high){
            quickSort(arr, k+1, high);
        }

        if (k > low){
            quickSort(arr, low ,k-1);
        }
    }
    
    public static void quickSortNonRecursion(int[] arr, int low, int high){
    //非递归，使用stack保存partition返回值
           if (arr == null || low < 0 || high <= 0 || low>high)
               return;
           Stack<Integer> temp = new Stack<>();
           int i, j;
           //（注意保存顺序）先将初始状态的左右指针压栈
           temp.push(high);//先存右指针
           temp.push(low);//再存左指针
           while (!temp.empty()) {
               i = temp.pop();//先弹出左指针
               j = temp.pop();//再弹出右指针
               if (i < j) {
                   int k = partition(arr, i, j);
                   if (k > i) {
                       temp.push(k - 1);//保存中间变量
                       temp.push(i);  //保存中间变量
                   }
                   if (j > k) {
                       temp.push(j);
                       temp.push(k + 1);
                   }
               }

           }
           }


    public static void main(String[] args){
        int[] arr = {8,4,5,1,3,66,6,6};
        quickSort(arr, 0, arr.length-1);

        for (int i : arr){
            System.out.println(i);
        }
    }
}