国外版

算法题（国外版）/bulb-switcher.html

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+<p>There are <code>n</code> bulbs that are initially off. You first turn on all the bulbs, then&nbsp;you turn off every second bulb.</p>
+
+<p>On the third round, you toggle every third bulb (turning on if it&#39;s off or turning off if it&#39;s on). For the <code>i<sup>th</sup></code> round, you toggle every <code>i</code> bulb. For the <code>n<sup>th</sup></code> round, you only toggle the last bulb.</p>
+
+<p>Return <em>the number of bulbs that are on after <code>n</code> rounds</em>.</p>
+
+<p>&nbsp;</p>
+<p><strong>Example 1:</strong></p>
+<img alt="" src="https://assets.leetcode.com/uploads/2020/11/05/bulb.jpg" style="width: 421px; height: 321px;" />
+<pre>
+<strong>Input:</strong> n = 3
+<strong>Output:</strong> 1
+<strong>Explanation:</strong> At first, the three bulbs are [off, off, off].
+After the first round, the three bulbs are [on, on, on].
+After the second round, the three bulbs are [on, off, on].
+After the third round, the three bulbs are [on, off, off]. 
+So you should return 1 because there is only one bulb is on.</pre>
+
+<p><strong>Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> n = 0
+<strong>Output:</strong> 0
+</pre>
+
+<p><strong>Example 3:</strong></p>
+
+<pre>
+<strong>Input:</strong> n = 1
+<strong>Output:</strong> 1
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>0 &lt;= n &lt;= 10<sup>9</sup></code></li>
+</ul>