Python | Leetcode Python题解之第446题等差数列划分II-子序列
题目：
题解：
class Solution:
def numberOfArithmeticSlices(self, nums: List[int]) -> int:
ans = 0
f = [defaultdict(int) for _ in nums]
for i, x in enumerate(nums):
for j in range(i):
d = x - nums[j]
cnt = f[j][d]
ans += cnt
f[i][d] += cnt + 1
return ans