Count Almost Equal Pairs I
<p>You are given an array <code>nums</code> consisting of positive integers.</p>

<p>We call two integers <code>x</code> and <code>y</code> in this problem <strong>almost equal</strong> if both integers can become equal after performing the following operation <strong>at most once</strong>:</p>

<ul>
	<li>Choose <strong>either</strong> <code>x</code> or <code>y</code> and swap any two digits within the chosen number.</li>
</ul>

<p>Return the number of indices <code>i</code> and <code>j</code> in <code>nums</code> where <code>i &lt; j</code> such that <code>nums[i]</code> and <code>nums[j]</code> are <strong>almost equal</strong>.</p>

<p><strong>Note</strong> that it is allowed for an integer to have leading zeros after performing an operation.</p>

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

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">nums = [3,12,30,17,21]</span></p>

<p><strong>Output:</strong> <span class="example-io">2</span></p>

<p><strong>Explanation:</strong></p>

<p>The almost equal pairs of elements are:</p>

<ul>
	<li>3 and 30. By swapping 3 and 0 in 30, you get 3.</li>
	<li>12 and 21. By swapping 1 and 2 in 12, you get 21.</li>
</ul>
</div>

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

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">nums = [1,1,1,1,1]</span></p>

<p><strong>Output:</strong> <span class="example-io">10</span></p>

<p><strong>Explanation:</strong></p>

<p>Every two elements in the array are almost equal.</p>
</div>

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

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">nums = [123,231]</span></p>

<p><strong>Output:</strong> <span class="example-io">0</span></p>

<p><strong>Explanation:</strong></p>

<p>We cannot swap any two digits of 123 or 231 to reach the other.</p>
</div>

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

<ul>
	<li><code>2 &lt;= nums.length &lt;= 100</code></li>
	<li><code>1 &lt;= nums[i] &lt;= 10<sup>6</sup></code></li>
</ul>
Array; Hash Table; Counting; Enumeration; Sorting
func countPairs(nums []int) (ans int) {
	sort.Ints(nums)
	cnt := make(map[int]int)

	for _, x := range nums {
		vis := make(map[int]struct{})
		vis[x] = struct{}{}
		s := []rune(strconv.Itoa(x))

		for j := 0; j < len(s); j++ {
			for i := 0; i < j; i++ {
				s[i], s[j] = s[j], s[i]
				y, _ := strconv.Atoi(string(s))
				vis[y] = struct{}{}
				s[i], s[j] = s[j], s[i]
			}
		}

		for y := range vis {
			ans += cnt[y]
		}
		cnt[x]++
	}

	return
}
