413. Arithmetic Slices

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.

一道DP基础题，将每一步的记录在数组中就好，例如：

[1,2]     DP=[0,0]
[1,2,3]    DP=[0,0,1]   [1,2,3]
[1,2,3,4]  DP=[0,0,1,2]   [2,3,4] [1,2,3,4]
[1,2,3,4,5] DP=[0,0,1,2,3]  [3,4,5] [2,3,4,5] [1,2,3,4,5]
···
具体解法
class Solution(object):
    def numberOfArithmeticSlices(self, A):
        """
        :type A: List[int]
        :rtype: int
        """
        dp = [0 for i in range(len(A))]
        for i in range(2,len(A)):
            if A[i]-A[i-1] == A[i-1]-A[i-2]:
                dp[i] = dp[i-1]+1
            else:
                dp[i] = 0
        return sum(dp)