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 {
    public int[] relativeSortArray(int[] arr1, int[] arr2) {
        Map<Integer, Integer> pos = new HashMap<>(arr2.length);
        for (int i = 0; i < arr2.length; ++i) {
            pos.put(arr2[i], i);
        }
        int[][] arr = new int[arr1.length][0];
        for (int i = 0; i < arr.length; ++i) {
            arr[i] = new int[] {arr1[i], pos.getOrDefault(arr1[i], arr2.length + arr1[i])};
        }
        Arrays.sort(arr, (a, b) -> a[1] - b[1]);
        for (int i = 0; i < arr.length; ++i) {
            arr1[i] = arr[i][0];
        }
        return arr1;
    }
}