<p>Strings <code>s1</code> and <code>s2</code> are <code>k</code><strong>-similar</strong> (for some non-negative integer <code>k</code>) if we can swap the positions of two letters in <code>s1</code> exactly <code>k</code> times so that the resulting string equals <code>s2</code>.</p>

<p>Given two anagrams <code>s1</code> and <code>s2</code>, return the smallest <code>k</code> for which <code>s1</code> and <code>s2</code> are <code>k</code><strong>-similar</strong>.</p>

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

<pre>
<strong>Input:</strong> s1 = &quot;ab&quot;, s2 = &quot;ba&quot;
<strong>Output:</strong> 1
<strong>Explanation:</strong> The two string are 1-similar because we can use one swap to change s1 to s2: &quot;ab&quot; --&gt; &quot;ba&quot;.
</pre>

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

<pre>
<strong>Input:</strong> s1 = &quot;abc&quot;, s2 = &quot;bca&quot;
<strong>Output:</strong> 2
<strong>Explanation:</strong> The two strings are 2-similar because we can use two swaps to change s1 to s2: &quot;abc&quot; --&gt; &quot;bac&quot; --&gt; &quot;bca&quot;.
</pre>

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

<ul>
	<li><code>1 &lt;= s1.length &lt;= 20</code></li>
	<li><code>s2.length == s1.length</code></li>
	<li><code>s1</code> and <code>s2</code> contain only lowercase letters from the set <code>{&#39;a&#39;, &#39;b&#39;, &#39;c&#39;, &#39;d&#39;, &#39;e&#39;, &#39;f&#39;}</code>.</li>
	<li><code>s2</code> is an anagram of <code>s1</code>.</li>
</ul>

class Solution {
public:
    int kSimilarity(string s1, string s2) {
     
        std::queue<std::pair<std::string, int>> bfs_queue;
        std::map<std::string, int> visited_map;
        
        bfs_queue.push({s1, 0});
        visited_map[s1] = 1;
        
        while(!bfs_queue.empty())
        {
            std::string current_node = bfs_queue.front().first;
            int current_level = bfs_queue.front().second;
            bfs_queue.pop();
            
            if(current_node == s2)
            {
                return current_level;
            }
            
            for(int i = 0; i < current_node.size(); ++i)
            {
                if(current_node.at(i) != s2.at(i))
                {
                    for(int j = i + 1; j < current_node.size(); ++j)
                    {
                        if(current_node.at(j) != s2.at(j) && current_node.at(j) == s2.at(i))
                        {
                            std::string adjacent_node = current_node;
                            char c = adjacent_node.at(i);
                            adjacent_node.at(i) = adjacent_node.at(j);
                            adjacent_node.at(j) = c;
                            
                            if(visited_map.find(adjacent_node) == visited_map.end())
                            {
                                visited_map[adjacent_node] = 1;
                                bfs_queue.push({adjacent_node, 1 + current_level});
                            }
                        }
                    }
                    break;
                }
            }
        }
        
        return -1;
    }
};
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