Solution3.java

class Solution {
    private int[] nums;

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

    private void mergeSort(int l, int r) {
        if (l >= r) {
            return;
        }
        int mid = (l + r) >> 1;
        mergeSort(l, mid);
        mergeSort(mid + 1, r);
        int i = l, j = mid + 1, k = 0;
        int[] tmp = new int[r - l + 1];
        while (i <= mid && j <= r) {
            if (nums[i] <= nums[j]) {
                tmp[k++] = nums[i++];
            } else {
                tmp[k++] = nums[j++];
            }
        }
        while (i <= mid) {
            tmp[k++] = nums[i++];
        }
        while (j <= r) {
            tmp[k++] = nums[j++];
        }
        for (i = l; i <= r; ++i) {
            nums[i] = tmp[i - l];
        }
    }
}