<p>Given an integer array <code>nums</code> and an integer <code>k</code>, return <em>the number of pairs</em> <code>(i, j)</code> <em>where</em> <code>i &lt; j</code> <em>such that</em> <code>|nums[i] - nums[j]| == k</code>.</p>

<p>The value of <code>|x|</code> is defined as:</p>

<ul>
	<li><code>x</code> if <code>x &gt;= 0</code>.</li>
	<li><code>-x</code> if <code>x &lt; 0</code>.</li>
</ul>

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

<pre>
<strong>Input:</strong> nums = [1,2,2,1], k = 1
<strong>Output:</strong> 4
<strong>Explanation:</strong> The pairs with an absolute difference of 1 are:
- [<strong><u>1</u></strong>,<strong><u>2</u></strong>,2,1]
- [<strong><u>1</u></strong>,2,<strong><u>2</u></strong>,1]
- [1,<strong><u>2</u></strong>,2,<strong><u>1</u></strong>]
- [1,2,<strong><u>2</u></strong>,<strong><u>1</u></strong>]
</pre>

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

<pre>
<strong>Input:</strong> nums = [1,3], k = 3
<strong>Output:</strong> 0
<strong>Explanation:</strong> There are no pairs with an absolute difference of 3.
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> nums = [3,2,1,5,4], k = 2
<strong>Output:</strong> 3
<b>Explanation:</b> The pairs with an absolute difference of 2 are:
- [<strong><u>3</u></strong>,2,<strong><u>1</u></strong>,5,4]
- [<strong><u>3</u></strong>,2,1,<strong><u>5</u></strong>,4]
- [3,<strong><u>2</u></strong>,1,5,<strong><u>4</u></strong>]
</pre>

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

<ul>
	<li><code>1 &lt;= nums.length &lt;= 200</code></li>
	<li><code>1 &lt;= nums[i] &lt;= 100</code></li>
	<li><code>1 &lt;= k &lt;= 99</code></li>
</ul>

class Solution:
    # def occurrences(s, lst):
    #     return (i for i,e in enumerate(lst) if e == s)

    def countKDifference(self, nums: List[int], k: int) -> int:
        freq = {}
        for num in nums:
            freq[num] = freq.get(num, 0) + 1
            
        count = 0
        for num in nums:
            complement = num + k
            if complement in freq:
                count += freq[complement] - (1 if num == complement else 0)
        
        return count % (10**9 + 7)

        # for num in nums:
        #     complement = num + k

        #     new_freq = list(i for i,e in enumerate(nums) if e == complement)
        #     count = count + len(new_freq)
        
        # return count % (10**9 + 7)
49