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
func relativeSortArray(arr1 []int, arr2 []int) []int {
	pos := map[int]int{}
	for i, x := range arr2 {
		pos[x] = i
	}
	arr := make([][2]int, len(arr1))
	for i, x := range arr1 {
		if p, ok := pos[x]; ok {
			arr[i] = [2]int{p, x}
		} else {
			arr[i] = [2]int{len(arr2), x}
		}
	}
	sort.Slice(arr, func(i, j int) bool {
		return arr[i][0] < arr[j][0] || arr[i][0] == arr[j][0] && arr[i][1] < arr[j][1]
	})
	for i, x := range arr {
		arr1[i] = x[1]
	}
	return arr1
}