Solution2.java

class Solution {
    private int[] nums;

    public int[] sortArray(int[] nums) {
        this.nums = nums;
        quickSort(0, nums.length - 1);
        return nums;
    }

    private void quickSort(int l, int r) {
        if (l >= r) {
            return;
        }
        int i = l - 1, j = r + 1, k = l;
        int x = nums[(l + r) >> 1];
        while (k < j) {
            if (nums[k] < x) {
                swap(++i, k++);
            } else if (nums[k] > x) {
                swap(--j, k);
            } else {
                ++k;
            }
        }
        quickSort(l, i);
        quickSort(j, r);
    }

    private void swap(int i, int j) {
        int t = nums[i];
        nums[i] = nums[j];
        nums[j] = t;
    }
}