<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>

class Solution {
public:
    int integerReplacement(int n) {
        if (n == 1) return 0;
        queue<long> q;
        unordered_set<long> visited;
        q.push(n);
        visited.insert(n);
        int steps = 0;
        while (!q.empty()) {
            int size = q.size();
            for (int i = 0; i < size; ++i) {
                long current = q.front();
                q.pop();
                if (current == 1) return steps;
                if (current % 2 == 0) {
                    if (visited.find(current / 2) == visited.end()) {
                        q.push(current / 2);
                        visited.insert(current / 2);
                    }
                } else {
                    if (visited.find(current + 1) == visited.end()) {
                        q.push(current + 1);
                        visited.insert(current + 1);
                    }
                    if (visited.find(current - 1) == visited.end()) {
                        q.push(current - 1);
                        visited.insert(current - 1);
                    }
                }
            }
            ++steps;
        }
        return 0;
    }
};
8100