Jump Game IV
<p>Given an array of&nbsp;integers <code>arr</code>, you are initially positioned at the first index of the array.</p>

<p>In one step you can jump from index <code>i</code> to index:</p>

<ul>
	<li><code>i + 1</code> where:&nbsp;<code>i + 1 &lt; arr.length</code>.</li>
	<li><code>i - 1</code> where:&nbsp;<code>i - 1 &gt;= 0</code>.</li>
	<li><code>j</code> where: <code>arr[i] == arr[j]</code> and <code>i != j</code>.</li>
</ul>

<p>Return <em>the minimum number of steps</em> to reach the <strong>last index</strong> of the array.</p>

<p>Notice that you can not jump outside of the array at any time.</p>

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

<pre>
<strong>Input:</strong> arr = [100,-23,-23,404,100,23,23,23,3,404]
<strong>Output:</strong> 3
<strong>Explanation:</strong> You need three jumps from index 0 --&gt; 4 --&gt; 3 --&gt; 9. Note that index 9 is the last index of the array.
</pre>

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

<pre>
<strong>Input:</strong> arr = [7]
<strong>Output:</strong> 0
<strong>Explanation:</strong> Start index is the last index. You do not need to jump.
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> arr = [7,6,9,6,9,6,9,7]
<strong>Output:</strong> 1
<strong>Explanation:</strong> You can jump directly from index 0 to index 7 which is last index of the array.
</pre>

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

<ul>
	<li><code>1 &lt;= arr.length &lt;= 5 * 10<sup>4</sup></code></li>
	<li><code>-10<sup>8</sup> &lt;= arr[i] &lt;= 10<sup>8</sup></code></li>
</ul>
Breadth-First Search; Array; Hash Table
class Solution {
    public int minJumps(int[] arr) {
        Map<Integer, List<Integer>> g = new HashMap<>();
        int n = arr.length;
        for (int i = 0; i < n; i++) {
            g.computeIfAbsent(arr[i], k -> new ArrayList<>()).add(i);
        }
        boolean[] vis = new boolean[n];
        Deque<Integer> q = new ArrayDeque<>();
        q.offer(0);
        vis[0] = true;
        for (int ans = 0;; ++ans) {
            for (int k = q.size(); k > 0; --k) {
                int i = q.poll();
                if (i == n - 1) {
                    return ans;
                }
                for (int j : g.get(arr[i])) {
                    if (!vis[j]) {
                        vis[j] = true;
                        q.offer(j);
                    }
                }
                g.get(arr[i]).clear();
                for (int j : new int[] {i - 1, i + 1}) {
                    if (0 <= j && j < n && !vis[j]) {
                        vis[j] = true;
                        q.offer(j);
                    }
                }
            }
        }
    }
}
