public int partitionArray(int[] nums, int k) {
        //write your code here
        if (nums == null || nums.length == 0)
        return 0;
        int left = 0;
        int right = nums.length - 1;
        while (left <= right) {
            while (left <= right && nums[left] < k) {
                left++;
            }
            while (left <= right && nums[right] >= k) {
                right--;
            }
            if (left <= right) {
                int temp = nums[left];
                nums[left] = nums[right];
                nums[right] = temp;
                left++;
                right--;
            }
        }
        return left;
    }