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1995. Count Special Quadruplets

Difficulty Topics

Description

Given a 0-indexed integer array nums, return the number of distinct quadruplets (a, b, c, d) such that:

  • nums[a] + nums[b] + nums[c] == nums[d], and
  • a < b < c < d

 

Example 1:

Input: nums = [1,2,3,6]
Output: 1
Explanation: The only quadruplet that satisfies the requirement is (0, 1, 2, 3) because 1 + 2 + 3 == 6.

Example 2:

Input: nums = [3,3,6,4,5]
Output: 0
Explanation: There are no such quadruplets in [3,3,6,4,5].

Example 3:

Input: nums = [1,1,1,3,5]
Output: 4
Explanation: The 4 quadruplets that satisfy the requirement are:
- (0, 1, 2, 3): 1 + 1 + 1 == 3
- (0, 1, 3, 4): 1 + 1 + 3 == 5
- (0, 2, 3, 4): 1 + 1 + 3 == 5
- (1, 2, 3, 4): 1 + 1 + 3 == 5

 

Constraints:

  • 4 <= nums.length <= 50
  • 1 <= nums[i] <= 100

Solution

count-special-quadruplets.py
class Solution:
    def countQuadruplets(self, nums: List[int]) -> int:
        n = len(nums)
        res = 0

        for i in range(n):
            for j in range(i + 1, n):
                for k in range(j + 1, n):
                    for z in range(k + 1, n):
                        if nums[i] + nums[j] + nums[k] == nums[z]:
                            res += 1

        return res