Count Special Quadruplets LeetCode solution in Java

1
class Solution {
2
  public int countQuadruplets(int[] nums) {
3
    int res = 0;
4
    int len = nums.length;
5

6
    Map<Integer, Integer> count = new HashMap<>();
7
    count.put(nums[len - 1] - nums[len - 2], 1);
8

9
    for (int b = len - 3; b >= 1; b--) {
10
      for (int a = b - 1; a >= 0; a--) {
11
        res += count.getOrDefault(nums[a] + nums[b], 0);
12
      }
13

14
      for (int x = len - 1; x > b; x--) {
15
        count.put(nums[x] - nums[b], count.getOrDefault(nums[x] - nums[b], 0) + 1);
16
      }
17
    }
18

19
    return res;
20
  }
21
}