valid-subarrays-with-matching-sum-digits-i

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Algorithms

You are given an integer array <code>nums</code> and an integer digit <code>x</code>.

A subarray <code>nums[l..r]</code> is considered valid if the sum of its elements satisfies both of the following conditions:

<ul>
	<li>The first digit of the sum is equal to <code>x</code>.</li>
	<li>The last digit of the sum is equal to <code>x</code>.</li>
</ul>

Return the number of valid subarrays.

&nbsp;
Example 1:

<div class="example-block">
Input: nums = [1,100,1], x = 1

Output: 4

Explanation:

The valid subarrays are:

<ul>
	<li><code>nums[0..0]</code>: <code>sum = 1</code></li>
	<li><code>nums[0..1]</code>: <code>sum = 1 + 100 = 101</code></li>
	<li><code>nums[1..2]</code>: <code>sum = 100 + 1 = 101</code></li>
	<li><code>nums[2..2]</code>: <code>sum = 1</code></li>
</ul>

Thus, the answer is 4.
</div>

Example 2:

<div class="example-block">
Input: nums = [1], x = 2

Output: 0

Explanation:

The only subarray is <code>nums[0..0]</code> with a sum of 1, which does not satisfy the conditions.

Thus, the answer is 0.
</div>

&nbsp;
Constraints:

<ul>
	<li><code>1 &lt;= nums.length &lt;= 1500</code></li>
	<li><code>1 &lt;= nums[i] &lt;= 109</code></li>
	<li><code>1 &lt;= x &lt;= 9</code></li>
</ul>