Relative Sort Array
<p>Given two arrays <code>arr1</code> and <code>arr2</code>, the elements of <code>arr2</code> are distinct, and all elements in <code>arr2</code> are also in <code>arr1</code>.</p>

<p>Sort the elements of <code>arr1</code> such that the relative ordering of items in <code>arr1</code> are the same as in <code>arr2</code>. Elements that do not appear in <code>arr2</code> should be placed at the end of <code>arr1</code> in <strong>ascending</strong> order.</p>

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

<pre>
<strong>Input:</strong> arr1 = [2,3,1,3,2,4,6,7,9,2,19], arr2 = [2,1,4,3,9,6]
<strong>Output:</strong> [2,2,2,1,4,3,3,9,6,7,19]
</pre>

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

<pre>
<strong>Input:</strong> arr1 = [28,6,22,8,44,17], arr2 = [22,28,8,6]
<strong>Output:</strong> [22,28,8,6,17,44]
</pre>

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

<ul>
	<li><code>1 &lt;= arr1.length, arr2.length &lt;= 1000</code></li>
	<li><code>0 &lt;= arr1[i], arr2[i] &lt;= 1000</code></li>
	<li>All the elements of <code>arr2</code> are <strong>distinct</strong>.</li>
	<li>Each&nbsp;<code>arr2[i]</code> is in <code>arr1</code>.</li>
</ul>
Array; Hash Table; Counting Sort; Sorting
class Solution {
    func relativeSortArray(_ arr1: [Int], _ arr2: [Int]) -> [Int] {
        var pos = [Int: Int]()
        for (i, x) in arr2.enumerated() {
            pos[x] = i
        }
        var arr = [(Int, Int)]()
        for x in arr1 {
            let j = pos[x] ?? arr2.count
            arr.append((j, x))
        }
        arr.sort { $0.0 < $1.0 || ($0.0 == $1.0 && $0.1 < $1.1) }
        return arr.map { $0.1 }
    }
}
