Largest Palindromic Number
<p>You are given a string <code>num</code> consisting of digits only.</p>

<p>Return <em>the <strong>largest palindromic</strong> integer (in the form of a string) that can be formed using digits taken from </em><code>num</code>. It should not contain <strong>leading zeroes</strong>.</p>

<p><strong>Notes:</strong></p>

<ul>
	<li>You do <strong>not</strong> need to use all the digits of <code>num</code>, but you must use <strong>at least</strong> one digit.</li>
	<li>The digits can be reordered.</li>
</ul>

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

<pre>
<strong>Input:</strong> num = &quot;444947137&quot;
<strong>Output:</strong> &quot;7449447&quot;
<strong>Explanation:</strong> 
Use the digits &quot;4449477&quot; from &quot;<u><strong>44494</strong></u><u><strong>7</strong></u>13<u><strong>7</strong></u>&quot; to form the palindromic integer &quot;7449447&quot;.
It can be shown that &quot;7449447&quot; is the largest palindromic integer that can be formed.
</pre>

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

<pre>
<strong>Input:</strong> num = &quot;00009&quot;
<strong>Output:</strong> &quot;9&quot;
<strong>Explanation:</strong> 
It can be shown that &quot;9&quot; is the largest palindromic integer that can be formed.
Note that the integer returned should not contain leading zeroes.
</pre>

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

<ul>
	<li><code>1 &lt;= num.length &lt;= 10<sup>5</sup></code></li>
	<li><code>num</code> consists of digits.</li>
</ul>
Greedy; Hash Table; String; Counting
func largestPalindromic(num string) string {
	cnt := make([]int, 10)
	for _, c := range num {
		cnt[c-'0']++
	}
	ans := ""
	for i := 9; i >= 0; i-- {
		if cnt[i]%2 == 1 {
			ans = strconv.Itoa(i)
			cnt[i]--
			break
		}
	}
	for i := 0; i < 10; i++ {
		if cnt[i] > 0 {
			cnt[i] >>= 1
			s := strings.Repeat(strconv.Itoa(i), cnt[i])
			ans = s + ans + s
		}
	}
	ans = strings.Trim(ans, "0")
	if ans == "" {
		return "0"
	}
	return ans
}