<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 {
public:
    vector<string> keys={"","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};
    vector<string> ans;
     void helper(string digits,int index,string tempans){
        if(index==digits.size()){
            if(tempans.size()!=0){
            ans.push_back(tempans);}
            return;
        }
        else {
            for(int j=0;j<keys[digits[index]-'0'].size();j++){
                // '1' ko int(1) karne se nahi hoga bhai minus '0' karo you will get extact value then x=0+y;
                
                helper(digits,index+1,tempans+keys[digits[index]-'0'][j]);
            }
        }
     }
    vector<string> letterCombinations(string digits) {
        string tempans="";
        helper(digits,0,tempans);
        return ans;

    }
};
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