<p>You are given an alphanumeric string <code>s</code>. (<strong>Alphanumeric string</strong> is a string consisting of lowercase English letters and digits).</p>

<p>You have to find a permutation of the string where no letter is followed by another letter and no digit is followed by another digit. That is, no two adjacent characters have the same type.</p>

<p>Return <em>the reformatted string</em> or return <strong>an empty string</strong> if it is impossible to reformat the string.</p>

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

<pre>
<strong>Input:</strong> s = &quot;a0b1c2&quot;
<strong>Output:</strong> &quot;0a1b2c&quot;
<strong>Explanation:</strong> No two adjacent characters have the same type in &quot;0a1b2c&quot;. &quot;a0b1c2&quot;, &quot;0a1b2c&quot;, &quot;0c2a1b&quot; are also valid permutations.
</pre>

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

<pre>
<strong>Input:</strong> s = &quot;leetcode&quot;
<strong>Output:</strong> &quot;&quot;
<strong>Explanation:</strong> &quot;leetcode&quot; has only characters so we cannot separate them by digits.
</pre>

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

<pre>
<strong>Input:</strong> s = &quot;1229857369&quot;
<strong>Output:</strong> &quot;&quot;
<strong>Explanation:</strong> &quot;1229857369&quot; has only digits so we cannot separate them by characters.
</pre>

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

<ul>
	<li><code>1 &lt;= s.length &lt;= 500</code></li>
	<li><code>s</code> consists of only lowercase English letters and/or digits.</li>
</ul>

class Solution {
public:
    string reformat(string s) {
        vector<char> alpha;
        vector<char> numbers;
        // Creating a vector for storing alpha and numeric separately
        for(int i=0 ; i<s.size() ; i++)
        {
            if(s[i] >= 'a' && s[i] <= 'z'){
                alpha.push_back(s[i]);
            }
            else if(s[i] >= '0' && s[i] <= '9'){
                numbers.push_back(s[i]);
            }
        }
        string ans = "";
        int m = alpha.size();
        int n = numbers.size();
        // The number of alpha and numeric should be either equal or differ by 1 to make string valid
        if(abs(m-n) <= 1){
            if(m>=n){
                int i;
                for(i=0 ; i<n ; i++)
                {
                    ans += alpha[i];
                    ans += numbers[i];
                }
                if(m != n){
                    ans += alpha[i];
                }                
            }
            else{
                int i;
                for(i=0 ; i<m ; i++)
                {
                    ans += numbers[i];
                    ans += alpha[i];                    
                }
                ans += numbers[i];
            }
            
            return ans;    
        }
        // else string is invalid
        return ans;
    }
};
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