Subarray Sum equals K

Given an array of integers nums and an integer k, return the total number of subarrays whose sum equals to k.

A subarray is a contiguous non-empty sequence of elements within an array.

Example 1:

Input: nums = [1,1,1], k = 2

Output: 2

Example 2:

Input: nums = [1,2,3], k = 3

Output: 2

Constraints:

• 1 <= nums.length <= 2 * 104

• -1000 <= nums[i] <= 1000

• -107 <= k <= 107

class Solution {

    public int subarraySum(int[] nums, int k) {

        if (nums == null || nums.length == 0) return -1;

        int[] sums = new int[nums.length];  

        int sum = 0;

        for (int i = 0; i < nums.length; i++){

            sum += nums[i];

            sums[i] = sum;

        }

        int count = 0;

        for (int i = 0; i < nums.length; i++) {

            for (int j = i; j < nums.length; j++) {

                int current = nums[i] + (sums[j] - sums[i]);

                if (current == k){

                    count += 1;

                }

            }

        }

        return count;

    }

}

[1,3], k=1 => 1

[1,3], k=3 => 1

[1,3], k=4 => 1

[2,2], k=4 => 1

[2,2], k=2 => 2

[2,0,2], k=2 => 4

[0,0,1], k=1=> 3

[0,1,0], k=1=> 2

[0,1,1], k=1=> 3

[1,0,0], k=1=> 3

[1,0,1], k=1=> 4

[1,1,0], k=1=> 2

[1,1,1], k=1=> 3

[-1,0,1], k=0 => 2

[-1,1,0], k=0 => 3

[1,0,-1], k=0 => 2

[1,-1,0], k=0 => 3

[0,-1,1], k=0 => 3

[0,1,-1], k=0 => 3