ArithmeticSlices.cpp

/* Leetcode
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

*/
class Solution {
public:
    int numberOfArithmeticSlices(vector<int>& nums) {
        int n=nums.size();
        if(n<3)
            return 0;
        int diff=nums[1]-nums[0],str=0;
        int ans=0;
        for(int i=2;i<n;i++)
        {
            if(nums[i]-nums[i-1]==diff)
                continue;
            else
            {
                // starting from size 3
                int size=i-1-str+1;
                if(size>=3)
                {
                    int temp = ((size-2)*(size+1)) - ((size*(size+1))/2) +3;
                    ans+=temp;
                }
                str=i-1;
                diff=nums[i]-nums[i-1];
            }
        }
        int size=n-1-str+1;
        if(size>=3)
        {
            int temp = ((size-2)*(size+1)) - ((size*(size+1))/2) +3;
            ans+=temp;
        }
        return ans;
    }
};