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Description
tab: English
<p>Implement the <code>myAtoi(string s)</code> function, which converts a string to a 32-bit signed integer.</p>
<p>The algorithm for <code>myAtoi(string s)</code> is as follows:</p>
<ol>
<li><strong>Whitespace</strong>: Ignore any leading whitespace (<code>" "</code>).</li>
<li><strong>Signedness</strong>: Determine the sign by checking if the next character is <code>'-'</code> or <code>'+'</code>, assuming positivity if neither present.</li>
<li><strong>Conversion</strong>: Read the integer by skipping leading zeros until a non-digit character is encountered or the end of the string is reached. If no digits were read, then the result is 0.</li>
<li><strong>Rounding</strong>: If the integer is out of the 32-bit signed integer range <code>[-2<sup>31</sup>, 2<sup>31</sup> - 1]</code>, then round the integer to remain in the range. Specifically, integers less than <code>-2<sup>31</sup></code> should be rounded to <code>-2<sup>31</sup></code>, and integers greater than <code>2<sup>31</sup> - 1</code> should be rounded to <code>2<sup>31</sup> - 1</code>.</li>
</ol>
<p>Return the integer as the final result.</p>
<p> </p>
<p><strong class="example">Example 1:</strong></p>
<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">s = "42"</span></p>
<p><strong>Output:</strong> <span class="example-io">42</span></p>
<p><strong>Explanation:</strong></p>
<pre>
The underlined characters are what is read in and the caret is the current reader position.
Step 1: "42" (no characters read because there is no leading whitespace)
^
Step 2: "42" (no characters read because there is neither a '-' nor '+')
^
Step 3: "<u>42</u>" ("42" is read in)
^
</pre>
</div>
<p><strong class="example">Example 2:</strong></p>
<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">s = " -042"</span></p>
<p><strong>Output:</strong> <span class="example-io">-42</span></p>
<p><strong>Explanation:</strong></p>
<pre>
Step 1: "<u> </u>-042" (leading whitespace is read and ignored)
^
Step 2: " <u>-</u>042" ('-' is read, so the result should be negative)
^
Step 3: " -<u>042</u>" ("042" is read in, leading zeros ignored in the result)
^
</pre>
</div>
<p><strong class="example">Example 3:</strong></p>
<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">s = "1337c0d3"</span></p>
<p><strong>Output:</strong> <span class="example-io">1337</span></p>
<p><strong>Explanation:</strong></p>
<pre>
Step 1: "1337c0d3" (no characters read because there is no leading whitespace)
^
Step 2: "1337c0d3" (no characters read because there is neither a '-' nor '+')
^
Step 3: "<u>1337</u>c0d3" ("1337" is read in; reading stops because the next character is a non-digit)
^
</pre>
</div>
<p><strong class="example">Example 4:</strong></p>
<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">s = "0-1"</span></p>
<p><strong>Output:</strong> <span class="example-io">0</span></p>
<p><strong>Explanation:</strong></p>
<pre>
Step 1: "0-1" (no characters read because there is no leading whitespace)
^
Step 2: "0-1" (no characters read because there is neither a '-' nor '+')
^
Step 3: "<u>0</u>-1" ("0" is read in; reading stops because the next character is a non-digit)
^
</pre>
</div>
<p><strong class="example">Example 5:</strong></p>
<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">s = "words and 987"</span></p>
<p><strong>Output:</strong> <span class="example-io">0</span></p>
<p><strong>Explanation:</strong></p>
<p>Reading stops at the first non-digit character 'w'.</p>
</div>
<p> </p>
<p><strong>Constraints:</strong></p>
<ul>
<li><code>0 <= s.length <= 200</code></li>
<li><code>s</code> consists of English letters (lower-case and upper-case), digits (<code>0-9</code>), <code>' '</code>, <code>'+'</code>, <code>'-'</code>, and <code>'.'</code>.</li>
</ul>
---
[submissions](https://leetcode.com/problems/string-to-integer-atoi/submissions/) | [solutions](https://leetcode.com/problems/string-to-integer-atoi/solutions/)
tab: 中文
<p>请你来实现一个 <code>myAtoi(string s)</code> 函数，使其能将字符串转换成一个 32 位有符号整数。</p>
<p>函数 <code>myAtoi(string s)</code> 的算法如下：</p>
<ol>
<li><strong>空格：</strong>读入字符串并丢弃无用的前导空格（<code>" "</code>）</li>
<li><strong>符号：</strong>检查下一个字符（假设还未到字符末尾）为 <code>'-'</code> 还是 <code>'+'</code>。如果两者都不存在，则假定结果为正。</li>
<li><strong>转换：</strong>通过跳过前置零来读取该整数，直到遇到非数字字符或到达字符串的结尾。如果没有读取数字，则结果为0。</li>
<li><b>舍入：</b>如果整数数超过 32 位有符号整数范围 <code>[−2<sup>31</sup>, 2<sup>31 </sup>− 1]</code> ，需要截断这个整数，使其保持在这个范围内。具体来说，小于 <code>−2<sup>31</sup></code> 的整数应该被舍入为 <code>−2<sup>31</sup></code> ，大于 <code>2<sup>31 </sup>− 1</code> 的整数应该被舍入为 <code>2<sup>31 </sup>− 1</code> 。</li>
</ol>
<p>返回整数作为最终结果。</p>
<p> </p>
<p><strong class="example">示例 1：</strong></p>
<div class="example-block">
<p><strong>输入：</strong><span class="example-io">s = "42"</span></p>
<p><strong>输出：</strong><span class="example-io">42</span></p>
<p><strong>解释：</strong>加粗的字符串为已经读入的字符，插入符号是当前读取的字符。</p>
<pre>
带下划线线的字符是所读的内容，插入符号是当前读入位置。
第 1 步："42"（当前没有读入字符，因为没有前导空格）
^
第 2 步："42"（当前没有读入字符，因为这里不存在 '-' 或者 '+'）
^
第 3 步："<u>42</u>"（读入 "42"）
^
</pre>
</div>
<p><strong class="example">示例 2：</strong></p>
<div class="example-block">
<p><strong>输入：</strong><span class="example-io">s = " -042"</span></p>
<p><strong>输出：</strong><span class="example-io">-42</span></p>
<p><strong>解释：</strong></p>
<pre>
第 1 步："<u><strong> </strong></u>-042"（读入前导空格，但忽视掉）
^
第 2 步：" <u>-</u>042"（读入 '-' 字符，所以结果应该是负数）
^
第 3 步：" <u>-042</u>"（读入 "042"，在结果中忽略前导零）
^
</pre>
</div>
<p><strong class="example">示例 3：</strong></p>
<div class="example-block">
<p><strong>输入：</strong><span class="example-io">s = "</span>1337c0d3<span class="example-io">"</span></p>
<p><strong>输出：</strong><span class="example-io">1337</span></p>
<p><strong>解释：</strong></p>
<pre>
第 1 步："1337c0d3"（当前没有读入字符，因为没有前导空格）
^
第 2 步："1337c0d3"（当前没有读入字符，因为这里不存在 '-' 或者 '+'）
^
第 3 步："1337c0d3"（读入 "1337"；由于下一个字符不是一个数字，所以读入停止）
^
</pre>
</div>
<p><strong class="example">示例 4：</strong></p>
<div class="example-block">
<p><strong>输入：</strong><span class="example-io">s = "0-1"</span></p>
<p><span class="example-io"><b>输出：</b>0</span></p>
<p><strong>解释：</strong></p>
<pre>
第 1 步："0-1" (当前没有读入字符，因为没有前导空格)
^
第 2 步："0-1" (当前没有读入字符，因为这里不存在 '-' 或者 '+')
^
第 3 步："<u>0</u>-1" (读入 "0"；由于下一个字符不是一个数字，所以读入停止)
^
</pre>
</div>
<p><strong class="example">示例 5：</strong></p>
<div class="example-block">
<p><strong>输入：</strong><span class="example-io">s = "words and 987"</span></p>
<p><strong>输出：</strong><span class="example-io">0</span></p>
<p><strong>解释：</strong></p>
<p>读取在第一个非数字字符“w”处停止。</p>
</div>
<p> </p>
<p><strong>提示：</strong></p>
<ul>
<li><code>0 <= s.length <= 200</code></li>
<li><code>s</code> 由英文字母（大写和小写）、数字（<code>0-9</code>）、<code>' '</code>、<code>'+'</code>、<code>'-'</code> 和 <code>'.'</code> 组成</li>
</ul>
---
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