A sequence of number 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, these are arithmetic sequence:
1, 3, 5, 7, 9 7, 7, 7, 7 3, -1, -5, -9
The following sequence is not arithmetic.
1, 1, 2, 5, 7
A zero-indexed array A consisting of N numbers is given. A slice of that array is any pair of integers (P, Q) such that 0 <= P < Q < N.
A slice (P, Q) of array A is called arithmetic if the sequence:
A[P], A[p + 1], ..., A[Q - 1], A[Q] is arithmetic. In particular, this means that P + 1 < Q.
The function should return the number of arithmetic slices in the array A.
Example:
A = [1, 2, 3, 4] return: 3, for 3 arithmetic slices in A: [1, 2, 3], [2, 3, 4] and [1, 2, 3, 4] itself.
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刚开始一直没想出怎么做，但是它的通过率竟然这么干
今天又看了一眼，才发现，原来自己看错题了，人家要求的序列，必须是两两相邻的，中间不能隔着，那岂不是简单多了
之前以为是 隔着也可以呢
那这就很简单了
class Solution(object):
def numberOfArithmeticSlices(self, A):
if len(A) < 3:
return 0
res = 0
i = 2
l = 1
while i < len(A):
if (A[i-1] - A[i-2]) == (A[i] - A[i-1]):
res += l
l += 1
else:
l = 1
i += 1
return res