## DEV Community

Abhishek Chaudhary

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# Arithmetic Slices

An integer array is called arithmetic if it consists of at least three elements and if the difference between any two consecutive elements is the same.

• For example, `[1,3,5,7,9]`, `[7,7,7,7]`, and `[3,-1,-5,-9]` are arithmetic sequences.

Given an integer array `nums`, return the number of arithmetic subarrays of `nums`.

A subarray is a contiguous subsequence of the array.

Example 1:

Input: nums = [1,2,3,4]
Output: 3
Explanation: We have 3 arithmetic slices in nums: [1, 2, 3], [2, 3, 4] and [1,2,3,4] itself.

Example 2:

Input: nums = [1]
Output: 0

Constraints:

• `1 <= nums.length <= 5000`
• `-1000 <= nums[i] <= 1000`

SOLUTION:

``````class Solution:
def numSlicesEndingHere(self, nums, i, n):
if i in self.cache:
return self.cache[i]
if i < 2:
return 0
if i == 2:
if nums[2] - nums[1] == nums[1] - nums[0]:
self.cache[i] = 1
return 1
self.cache[i] = 0
return 0
if nums[i] - nums[i - 1] == nums[i - 1] - nums[i - 2]:
val = 1 + self.numSlicesEndingHere(nums, i - 1, n)
self.cache[i] = val
return val
self.cache[i] = 0
return 0

def numberOfArithmeticSlices(self, nums: List[int]) -> int:
n = len(nums)
self.cache = {}
ctr = 0
for i in range(n):
ctr += self.numSlicesEndingHere(nums, i, n)
return ctr
``````