<p>Given a string containing digits from <code>2-9</code> inclusive, return all possible letter combinations that the number could represent. Return the answer in <strong>any order</strong>.</p>

<p>A mapping of digits to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters.</p>
<img alt="" src="https://assets.leetcode.com/uploads/2022/03/15/1200px-telephone-keypad2svg.png" style="width: 300px; height: 243px;" />
<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> digits = &quot;23&quot;
<strong>Output:</strong> [&quot;ad&quot;,&quot;ae&quot;,&quot;af&quot;,&quot;bd&quot;,&quot;be&quot;,&quot;bf&quot;,&quot;cd&quot;,&quot;ce&quot;,&quot;cf&quot;]
</pre>

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

<pre>
<strong>Input:</strong> digits = &quot;&quot;
<strong>Output:</strong> []
</pre>

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

<pre>
<strong>Input:</strong> digits = &quot;2&quot;
<strong>Output:</strong> [&quot;a&quot;,&quot;b&quot;,&quot;c&quot;]
</pre>

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

<ul>
	<li><code>0 &lt;= digits.length &lt;= 4</code></li>
	<li><code>digits[i]</code> is a digit in the range <code>[&#39;2&#39;, &#39;9&#39;]</code>.</li>
</ul>

class Solution {
    void combination(vector<string> & result,string word,string digits,vector<string> values,int itr)
    {
        if(word.size()==digits.size())
        result.push_back(word);
        else
        {
            for(int i=0;i<values[digits[itr]-48].size();i++)
             combination(result,word+values[digits[itr]-48][i],digits,values,itr+1);
        }
    }
public:
    vector<string> letterCombinations(string digits) {
        vector<string> result;
        if(digits.size()==0)
        return result;
        // string values={"","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};
        vector<string> values;
        values.push_back("");
        values.push_back("");
        values.push_back("abc");
        values.push_back("def");
        values.push_back("ghi");
        values.push_back("jkl");
        values.push_back("mno");
        values.push_back("pqrs");
        values.push_back("tuv");
        values.push_back("wxyz");

        combination(result,"",digits,values,0);
        return result;
        
    }
};
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