An integer array 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,
[1,3,5,7,9],[7,7,7,7], and[3,-1,-5,-9]are arithmetic sequences.
Given an integer array nums, return the number of arithmetic subarrays of nums.
A subarray is a contiguous subsequence of the array.
Example 1:
Input: nums = [1,2,3,4] Output: 3 Explanation: We have 3 arithmetic slices in nums: [1, 2, 3], [2, 3, 4] and [1,2,3,4] itself.
Example 2:
Input: nums = [1] Output: 0
Constraints:
1 <= nums.length <= 5000-1000 <= nums[i] <= 1000
Dynamic programming.
class Solution:
def numberOfArithmeticSlices(self, nums: List[int]) -> int:
n = len(nums)
dp = [0] * n
for i in range(2, n):
if nums[i] + nums[i - 2] == (nums[i - 1] << 1):
dp[i] = 1 + dp[i - 1]
return sum(dp)class Solution {
public int numberOfArithmeticSlices(int[] nums) {
int n = nums.length;
int[] dp = new int[n];
for (int i = 2; i < n; ++i) {
if (nums[i] + nums[i - 2] == (nums[i - 1] << 1)) {
dp[i] = 1 + dp[i - 1];
}
}
int res = 0;
for (int e : dp) {
res += e;
}
return res;
}
}class Solution {
public:
int numberOfArithmeticSlices(vector<int>& nums) {
int n = nums.size();
vector<int> dp(n, 0);
for (int i = 2; i < n; ++i) {
if (nums[i] + nums[i - 2] == (nums[i - 1] * 2)) {
dp[i] = 1 + dp[i - 1];
}
}
int res = 0;
for (auto e : dp) {
res += e;
}
return res;
}
};func numberOfArithmeticSlices(nums []int) int {
n := len(nums)
dp := make([]int, n)
for i := 2; i < n; i++ {
if nums[i]-nums[i-1] == nums[i-1]-nums[i-2] {
dp[i] = 1 + dp[i-1]
}
}
res := 0
for _, e := range dp {
res += e
}
return res
}