快速排序 Quick Sort

public class QuickSort {
    public static void quickSort(int[] nums, int start, int end) {
        if(start >= end) {
            return;
        }
        int pivot = partition2(nums, start, end);
        quickSort(nums, start, pivot - 1);
        quickSort(nums, pivot + 1, end);
    }

    public static int partition(int[] nums, int start, int end) {
        int pivot = start;
        for(int i = start + 1; i <= end; i++) {
            if(nums[i] <= nums[start]) {
                pivot++;
                int temp = nums[pivot];
                nums[pivot] = nums[i];
                nums[i] = temp;
            }
        }
        int temp = nums[pivot];
        nums[pivot] = nums[start];
        nums[start] = temp;
        return pivot;
    }

//    better partition method
    public static int partition2(int[] nums, int start, int end) {
        int pivot = start, i = start + 1, j = end;
        while(i < j) {
            while(i <= end && nums[i] <= nums[pivot]) {
                i++;
            }
            while(nums[j] >nums[pivot]) {
                j--;
            }
            if(i >= j) {
                break;
            }
            int temp = nums[i];
            nums[i] = nums[j];
            nums[j] = temp;
        }
        i--;
        int temp = nums[i];
        nums[i] = nums[pivot];
        nums[pivot] = temp;
        return i;
    }

    public static void main(String[] args) {
        int[] nums = new int[]{13, 6, 9, 1, 19, -21, 5};
        quickSort(nums, 0, nums.length - 1);
        System.out.println(nums);
    }
}