Goat Latin
<p>You are given a string <code>sentence</code> that consist of words separated by spaces. Each word consists of lowercase and uppercase letters only.</p>

<p>We would like to convert the sentence to &quot;Goat Latin&quot; (a made-up language similar to Pig Latin.) The rules of Goat Latin are as follows:</p>

<ul>
	<li>If a word begins with a vowel (<code>&#39;a&#39;</code>, <code>&#39;e&#39;</code>, <code>&#39;i&#39;</code>, <code>&#39;o&#39;</code>, or <code>&#39;u&#39;</code>), append <code>&quot;ma&quot;</code> to the end of the word.

    <ul>
    	<li>For example, the word <code>&quot;apple&quot;</code> becomes <code>&quot;applema&quot;</code>.</li>
    </ul>
    </li>
    <li>If a word begins with a consonant (i.e., not a vowel), remove the first letter and append it to the end, then add <code>&quot;ma&quot;</code>.
    <ul>
    	<li>For example, the word <code>&quot;goat&quot;</code> becomes <code>&quot;oatgma&quot;</code>.</li>
    </ul>
    </li>
    <li>Add one letter <code>&#39;a&#39;</code> to the end of each word per its word index in the sentence, starting with <code>1</code>.
    <ul>
    	<li>For example, the first word gets <code>&quot;a&quot;</code> added to the end, the second word gets <code>&quot;aa&quot;</code> added to the end, and so on.</li>
    </ul>
    </li>

</ul>

<p>Return<em> the final sentence representing the conversion from sentence to Goat Latin</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre><strong>Input:</strong> sentence = "I speak Goat Latin"
<strong>Output:</strong> "Imaa peaksmaaa oatGmaaaa atinLmaaaaa"
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> sentence = "The quick brown fox jumped over the lazy dog"
<strong>Output:</strong> "heTmaa uickqmaaa rownbmaaaa oxfmaaaaa umpedjmaaaaaa overmaaaaaaa hetmaaaaaaaa azylmaaaaaaaaa ogdmaaaaaaaaaa"
</pre>
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= sentence.length &lt;= 150</code></li>
	<li><code>sentence</code> consists of English letters and spaces.</li>
	<li><code>sentence</code> has no leading or trailing spaces.</li>
	<li>All the words in <code>sentence</code> are separated by a single space.</li>
</ul>
String
class Solution {
    public String toGoatLatin(String sentence) {
        List<String> ans = new ArrayList<>();
        Set<Character> vowels
            = new HashSet<>(Arrays.asList('a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U'));
        int i = 1;
        for (String word : sentence.split(" ")) {
            StringBuilder t = new StringBuilder();
            if (!vowels.contains(word.charAt(0))) {
                t.append(word.substring(1));
                t.append(word.charAt(0));
            } else {
                t.append(word);
            }
            t.append("ma");
            for (int j = 0; j < i; ++j) {
                t.append("a");
            }
            ++i;
            ans.add(t.toString());
        }
        return String.join(" ", ans);
    }
}