<p>Given a positive integer <code>n</code>,&nbsp;you can apply one of the following&nbsp;operations:</p>

<ol>
	<li>If <code>n</code> is even, replace <code>n</code> with <code>n / 2</code>.</li>
	<li>If <code>n</code> is odd, replace <code>n</code> with either <code>n + 1</code> or <code>n - 1</code>.</li>
</ol>

<p>Return <em>the minimum number of operations needed for</em> <code>n</code> <em>to become</em> <code>1</code>.</p>

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

<pre>
<strong>Input:</strong> n = 8
<strong>Output:</strong> 3
<strong>Explanation:</strong> 8 -&gt; 4 -&gt; 2 -&gt; 1
</pre>

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

<pre>
<strong>Input:</strong> n = 7
<strong>Output:</strong> 4
<strong>Explanation: </strong>7 -&gt; 8 -&gt; 4 -&gt; 2 -&gt; 1
or 7 -&gt; 6 -&gt; 3 -&gt; 2 -&gt; 1
</pre>

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

<pre>
<strong>Input:</strong> n = 4
<strong>Output:</strong> 2
</pre>

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

<ul>
	<li><code>1 &lt;= n &lt;= 2<sup>31</sup> - 1</code></li>
</ul>

using ll = long long;
using pli = pair<ll, int>;
class Solution {
public:
    int integerReplacement(int n) {
        unordered_set<ll> vis;
        vis.insert(n);
        queue<pli> Q;
        Q.push({n, 0});
        while (Q.size()) {
            ll now = Q.front().first;
            int dist = Q.front().second;
            Q.pop();
            if (now == 1) return dist;
            if (now & 1) {
                for (auto& next : {now+1, now-1}) {
                    if (vis.count(next)) continue;
                    vis.insert(next);
                    Q.push({next, dist+1});
                }
            } else {
                ll next = now >> 1;
                if (vis.count(next)) continue;
                vis.insert(next);
                Q.push({next, dist+1});
            }
        }
        return 0;
    }
};
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