Arithmetic Slices
<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>
Array; Dynamic Programming; Sliding Window
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;
    }
}