leetcode-problemset/leetcode-cn/problem (English)/2出现的次数(English) [number-of-2s-in-range-lcci].html

<p>Write a method to count the number of 2s that appear in all the numbers between 0&nbsp;and n (inclusive).</p>

<p><strong>Example:</strong></p>

<pre>
<strong>Input: </strong>25
<strong>Output: </strong>9
<strong>Explanation: </strong>(2, 12, 20, 21, 22, 23, 24, 25)(Note that 22 counts for two 2s.)</pre>

<p>Note:</p>

<ul>
	<li><code>n &lt;= 10^9</code></li>
</ul>