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
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