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413. Arithmetic Slices

https://leetcode.com/problems/arithmetic-slices/

Python​

  • 4個元素的等差數列，可能組合為：
(4−3+1)+(4−4+1)=3(4-3+1)+(4-4+1) = 3
  • 5個元素的等差數列，可能組合為：
(5−3+1)+(5−4+1)+(5−5+1)=6(5-3+1)+(5-4+1)+(5-5+1) = 6
  • n個元素的等差數列，可能的組合為：
∑i=1n+1n\displaystyle\sum_{i=1}^{n+1} n 
class Solution:
    def numberOfArithmeticSlices(self, nums: List[int]) -> int:
        if len(nums) < 3:
            return 0

        arith_length = 0
        counter = 0

        for i in range(len(nums)-2):
            if nums[i+2] - nums[i+1] == nums[i+1] - nums[i]:
                arith_length += 1
                counter += arith_length
            else:
                arith_length = 0

        return counter