413. Arithmetic Slices

Description

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

Solutions

• class Solution {
public int numberOfArithmeticSlices(int[] nums) {
int ans = 0, cnt = 0;
int d = 3000;
for (int i = 0; i < nums.length - 1; ++i) {
if (nums[i + 1] - nums[i] == d) {
++cnt;
} else {
d = nums[i + 1] - nums[i];
cnt = 0;
}
ans += cnt;
}
return ans;
}
}

• class Solution {
public:
int numberOfArithmeticSlices(vector<int>& nums) {
int ans = 0, cnt = 0;
int d = 3000;
for (int i = 0; i < nums.size() - 1; ++i) {
if (nums[i + 1] - nums[i] == d) {
++cnt;
} else {
d = nums[i + 1] - nums[i];
cnt = 0;
}
ans += cnt;
}
return ans;
}
};

• class Solution:
def numberOfArithmeticSlices(self, nums: List[int]) -> int:
ans = cnt = 0
d = 3000
for a, b in pairwise(nums):
if b - a == d:
cnt += 1
else:
d = b - a
cnt = 0
ans += cnt
return ans


• func numberOfArithmeticSlices(nums []int) (ans int) {
cnt, d := 0, 3000
for i, b := range nums[1:] {
a := nums[i]
if b-a == d {
cnt++
} else {
d = b - a
cnt = 0
}
ans += cnt
}
return
}

• function numberOfArithmeticSlices(nums: number[]): number {
let ans = 0;
let cnt = 0;
let d = 3000;
for (let i = 0; i < nums.length - 1; ++i) {
const a = nums[i];
const b = nums[i + 1];
if (b - a == d) {
++cnt;
} else {
d = b - a;
cnt = 0;
}
ans += cnt;
}
return ans;
}