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
func minJumps(arr []int) int {
	g := map[int][]int{}
	for i, x := range arr {
		g[x] = append(g[x], i)
	}
	n := len(arr)
	q := []int{0}
	vis := make([]bool, n)
	vis[0] = true
	for ans := 0; ; ans++ {
		for k := len(q); k > 0; k-- {
			i := q[0]
			q = q[1:]
			if i == n-1 {
				return ans
			}
			for _, j := range g[arr[i]] {
				if !vis[j] {
					vis[j] = true
					q = append(q, j)
				}
			}
			g[arr[i]] = nil
			for _, j := range []int{i - 1, i + 1} {
				if 0 <= j && j < n && !vis[j] {
					vis[j] = true
					q = append(q, j)
				}
			}
		}
	}
}
