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Description
tab: English
<p>Given an integer <code>n</code>, return <em>the number of prime numbers that are strictly less than</em> <code>n</code>.</p>
<p> </p>
<p><strong class="example">Example 1:</strong></p>
<pre>
<strong>Input:</strong> n = 10
<strong>Output:</strong> 4
<strong>Explanation:</strong> There are 4 prime numbers less than 10, they are 2, 3, 5, 7.
</pre>
<p><strong class="example">Example 2:</strong></p>
<pre>
<strong>Input:</strong> n = 0
<strong>Output:</strong> 0
</pre>
<p><strong class="example">Example 3:</strong></p>
<pre>
<strong>Input:</strong> n = 1
<strong>Output:</strong> 0
</pre>
<p> </p>
<p><strong>Constraints:</strong></p>
<ul>
<li><code>0 <= n <= 5 * 10<sup>6</sup></code></li>
</ul>
> [!tip]- Hint 1
>
> Checking all the integers in the range [1, n - 1] is not efficient. Think about a better approach.
> [!tip]- Hint 2
>
> Since most of the numbers are not primes, we need a fast approach to exclude the non-prime integers.
> [!tip]- Hint 3
>
> Use Sieve of Eratosthenes.
---
[submissions](https://leetcode.com/problems/count-primes/submissions/) | [solutions](https://leetcode.com/problems/count-primes/solutions/)
tab: 中文
<p>给定整数 <code>n</code> ，返回 <em>所有小于非负整数 <code>n</code> 的质数的数量</em> 。</p>
<p> </p>
<p><strong>示例 1：</strong></p>
<pre>
<strong>输入：</strong>n = 10
<strong>输出：</strong>4
<strong>解释：</strong>小于 10 的质数一共有 4 个, 它们是 2, 3, 5, 7 。
</pre>
<p><strong>示例 2：</strong></p>
<pre>
<strong>输入：</strong>n = 0
<strong>输出：</strong>0
</pre>
<p><strong>示例 3：</strong></p>
<pre>
<strong>输入：</strong>n = 1
<strong>输出</strong>：0
</pre>
<p> </p>
<p><strong>提示：</strong></p>
<ul>
<li><code>0 <= n <= 5 * 10<sup>6</sup></code></li>
</ul>
> [!tip]- 提示 1
>
> Checking all the integers in the range [1, n - 1] is not efficient. Think about a better approach.
> [!tip]- 提示 2
>
> Since most of the numbers are not primes, we need a fast approach to exclude the non-prime integers.
> [!tip]- 提示 3
>
> Use Sieve of Eratosthenes.
---
[提交记录](https://leetcode.cn/problems/count-primes/submissions/) | [题解](https://leetcode.cn/problems/count-primes/solution/)
Solutions & Notes
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