1. 题目
一个数列的等差数列子数组有多少个。
A = [1, 2, 3, 4]返回: 3, A 中有三个子等差数组: [1, 2, 3], [2, 3, 4] 以及自身 [1, 2, 3, 4]。
2. 解题
状态公式
if(A[i]−A[i−1]=A[i−1]−A[i−2]),thendp[i]=dp[i−1]+1,i>=2if (A[i]-A[i-1] =A[i-1]-A[i-2]) , \quad then \quad dp[i] = dp[i-1]+1, i>=2if(A[i]−A[i−1]=A[i−1]−A[i−2]),thendp[i]=dp[i−1]+1,i>=2
class Solution {
public:int numberOfArithmeticSlices(vector<int>& A) {if(A.size() <= 2)return 0;int dp[A.size()] = {0}, differ = A[1]-A[0], sum = 0;for(int i = 2; i < A.size(); ++i){if(A[i]-A[i-1] == differ){dp[i] = dp[i-1]+1;sum += dp[i];}elsediffer = A[i]-A[i-1];}return sum;}
};
