等差数列划分

思路：见题解https://leetcode-cn.com/problems/arithmetic-slices/solution/deng-chai-shu-lie-hua-fen-by-leetcode/

class Solution(object):
    def numberOfArithmeticSlices(self, A):
        """
        :type A: List[int]
        :rtype: int
        """
        if len(A) <= 2:
            return 0
        dp = [0] * len(A)
        for i in range(2, len(A)):
            if A[i] - A[i-1] == A[i-1] - A[i-2]:
                dp[i] = 1 + dp[i-1]
        return sum(dp)