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
class Solution {
public:
    int countPairs(vector<int>& nums) {
        sort(nums.begin(), nums.end());
        int ans = 0;
        unordered_map<int, int> cnt;

        for (int x : nums) {
            unordered_set<int> vis = {x};
            string s = to_string(x);

            for (int j = 0; j < s.length(); ++j) {
                for (int i = 0; i < j; ++i) {
                    swap(s[i], s[j]);
                    vis.insert(stoi(s));
                    swap(s[i], s[j]);
                }
            }

            for (int y : vis) {
                ans += cnt[y];
            }
            cnt[x]++;
        }

        return ans;
    }
};
