3Sum Smaller

Given an array of n integers nums and a target, find the number of index triplets i, j, k with 0 <= i < j < k < n that satisfy the condition nums[i] + nums[j] + nums[k] < target.

Example:

Input: nums = [-2,0,1,3], and target = 2
Output: 2 
Explanation: Because there are two triplets which sums are less than 2:
             [-2,0,1]
             [-2,0,3]

Follow up: Could you solve it in O(n2) runtime?

class Solution {
    public int threeSumSmaller(int[] nums, int target) {
        
        
        if(nums == null || nums.length == 0)
            return 0;
        
        Arrays.sort(nums);
        
        int res = 0;
        
        for(int i = 0; i < nums.length - 2; i++ ){
            int m = i+1, n = nums.length-1;
            while(m < n){
                 int sum = nums[i]+nums[m]+nums[n];
            
                if(sum >= target){
                    n--;
                 }
                    
                else{
                    res += n - m;
                    m++;
                }
            }
        }
        
        return res;
    }
}