# LeetCode 413. Arithmetic Slices

## Description

https://leetcode.com/problems/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`.

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 = 
Output: 0
```

Constraints:

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

## Explanation

Iterate each number and to find all arithmetic slices starting from each number.

## Python Solution

``````class Solution:
def numberOfArithmeticSlices(self, nums: List[int]) -> int:
if len(nums) < 3:
return 0

results = []

for i in range(len(nums) - 1):
prev = nums[i]

diff = None

subarrays = [nums[i]]

for j in range(i + 1, len(nums)):
if diff == None:
diff = nums[j] - prev
prev = nums[j]
subarrays.append(nums[j])
else:
if nums[j] - prev == diff:
subarrays.append(nums[j])
prev = nums[j]

if len(subarrays) >= 3:
results.append(list(subarrays))
else:
break

return len(results)``````
• Time Complexity: O(N).
• Space Complexity: O(N).