<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 res, n;
    string s2;
    
    void sim(int i, int p, string s1)
    {
        if(i ==n)
        {
            res = min(res, p);
            return;
        }
        
        if(p >= res) return;
        
        int ok = 0;
        if(s1[i] == s2[i]) 
            sim(i+1, p, s1);
        else
        {
            for(int k=i+1; k<n; k++)
            if(s1[k] == s2[i] && s2[k ] == s1[i])
            {
                swap(s1[k], s1[i]), p++, ok=1; 
                sim(i+1, p, s1);
            }
        }
        
        if(s1 == s2) {res = min(res, p); return;}
        
        if(!ok)
        for(int j=i+1; j<n; j++)
        {
            if(s1[j] == s2[i] && s1[j] != s2[j])
            {
                swap(s1[j], s1[i]);
                
                sim(i+1, p+1, s1);
                
                swap(s1[j], s1[i]);
                
            }
        }
        return;
    }
    
    int kSimilarity(string s1, string s20) {
        
        res = 1000;
        n = s1.length();
        s2 = s20;
        
        int p = 0;
        
        sim(0, p, s1);
        
        return res;
    }
};
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