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
Solution
class Solution:
def countQuadruplets(self, nums: List[int]) -> int:
cnt = 0
l = len(nums)
for a in range(l):
for b in range(a + 1, l):
for c in range(b + 1, l):
for d in range(c + 1, l):
if a < b < c < d and nums[a] + nums[b] + nums[c] == nums[d]:
cnt += 1
return cnt