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
function minJumps(arr: number[]): number {
    const g: Map<number, number[]> = new Map();
    const n = arr.length;
    for (let i = 0; i < n; ++i) {
        if (!g.has(arr[i])) {
            g.set(arr[i], []);
        }
        g.get(arr[i])!.push(i);
    }
    let q: number[] = [0];
    const vis: boolean[] = Array(n).fill(false);
    vis[0] = true;
    for (let ans = 0; ; ++ans) {
        const nq: number[] = [];
        for (const i of q) {
            if (i === n - 1) {
                return ans;
            }
            for (const j of g.get(arr[i])!) {
                if (!vis[j]) {
                    vis[j] = true;
                    nq.push(j);
                }
            }
            g.get(arr[i])!.length = 0;
            for (const j of [i - 1, i + 1]) {
                if (j >= 0 && j < n && !vis[j]) {
                    vis[j] = true;
                    nq.push(j);
                }
            }
        }
        q = nq;
    }
}
