Count Special Triplets
You receive an integer array nums .
A special triplet is defined as a triplet of indices (i, j, k) such that:
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0 <= i < j < k < n, wheren = nums.length -
nums[i] == nums[j] * 2 -
nums[k] == nums[j] * 2
Produce the total number of special triplets in the array.
Since the answer may be large, produce it modulo 10^9+ 7 .
Input: nums = [6,3,6]
Output: 1
Explanation: The only special triplet is (i, j, k) = (0, 1, 2) , where:
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nums[0] = 6,nums[1] = 3,nums[2] = 6 -
nums[0] = nums[1] * 2 = 3 * 2 = 6 -
nums[2] = nums[1] * 2 = 3 * 2 = 6
Input: nums = [0,1,0,0]
Output: 1
Explanation: The only special triplet is (i, j, k) = (0, 2, 3) , where:
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nums[0] = 0,nums[2] = 0,nums[3] = 0 -
nums[0] = nums[2] * 2 = 0 * 2 = 0 -
nums[3] = nums[2] * 2 = 0 * 2 = 0
Input: nums = [8,4,2,8,4]
Output: 2
Explanation: There are exactly two special triplets:
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(i, j, k) = (0, 1, 3)-
nums[0] = 8,nums[1] = 4,nums[3] = 8 -
nums[0] = nums[1] * 2 = 4 * 2 = 8 -
nums[3] = nums[1] * 2 = 4 * 2 = 8
-
-
(i, j, k) = (1, 2, 4)-
nums[1] = 4,nums[2] = 2,nums[4] = 4 -
nums[1] = nums[2] * 2 = 2 * 2 = 4 -
nums[4] = nums[2] * 2 = 2 * 2 = 4
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Constraints
3 <= n == nums.length <= 10^50 <= nums[i] <= 10^5
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