Two Sum - Less than or equal to target Lintcode

public class Solution {
    /**
     * @param nums an array of integer
     * @param target an integer
     * @return an integer
     */
    public int twoSum5(int[] nums, int target) {
        if (nums == null || nums.length < 2) {
            return 0;
        }
        Arrays.sort(nums);
        int start = 0;
        int end = nums.length - 1;
        int count = 0;
        while (start < end) {
            if (nums[start] + nums[end] <= target) {
                count += end - start;
                start++;
            } else {
                end--;
            }
        }
        return count;
    }
}