<p>An integer array is called arithmetic if it consists of <strong>at least three elements</strong> and if the difference between any two consecutive elements is the same.</p>

<ul>
	<li>For example, <code>[1,3,5,7,9]</code>, <code>[7,7,7,7]</code>, and <code>[3,-1,-5,-9]</code> are arithmetic sequences.</li>
</ul>

<p>Given an integer array <code>nums</code>, return <em>the number of arithmetic <strong>subarrays</strong> of</em> <code>nums</code>.</p>

<p>A <strong>subarray</strong> is a contiguous subsequence of the array.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> nums = [1,2,3,4]
<strong>Output:</strong> 3
<strong>Explanation:</strong> We have 3 arithmetic slices in nums: [1, 2, 3], [2, 3, 4] and [1,2,3,4] itself.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> nums = [1]
<strong>Output:</strong> 0
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= nums.length &lt;= 5000</code></li>
	<li><code>-1000 &lt;= nums[i] &lt;= 1000</code></li>
</ul>

class Solution {
public:
    int numberOfArithmeticSlices(vector<int>& nums) {

        int n = nums.size();
        vector<int> dp_cnt(n, 0);// arithmetic cnt end at index i
        vector<int> dp_diff(n, 0);// diff with previous element

        dp_cnt[0] = 0;
        dp_diff[0] = 0;

        for(int i=1; i<n; i++){

            dp_diff[i] = nums[i] - nums[i-1];
            if(i-1>0){
                if(dp_diff[i] == dp_diff[i-1]){
                    dp_cnt[i] = dp_cnt[i-1]+1;
                }
                else{
                    dp_cnt[i] = 0;
                }
            }
            
        }
        
        int ans = 0;

        for(auto e: dp_cnt){
            ans+=e;
        }
        return ans;
    }
};
9500