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77 lines
3.8 KiB
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77 lines
3.8 KiB
HTML
<p>Implement the <code>myAtoi(string s)</code> function, which converts a string to a 32-bit signed integer (similar to C/C++'s <code>atoi</code> function).</p>
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<p>The algorithm for <code>myAtoi(string s)</code> is as follows:</p>
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<ol>
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<li>Read in and ignore any leading whitespace.</li>
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<li>Check if the next character (if not already at the end of the string) is <code>'-'</code> or <code>'+'</code>. Read this character in if it is either. This determines if the final result is negative or positive respectively. Assume the result is positive if neither is present.</li>
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<li>Read in next the characters until the next non-digit character or the end of the input is reached. The rest of the string is ignored.</li>
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<li>Convert these digits into an integer (i.e. <code>"123" -> 123</code>, <code>"0032" -> 32</code>). If no digits were read, then the integer is <code>0</code>. Change the sign as necessary (from step 2).</li>
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<li>If the integer is out of the 32-bit signed integer range <code>[-2<sup>31</sup>, 2<sup>31</sup> - 1]</code>, then clamp the integer so that it remains in the range. Specifically, integers less than <code>-2<sup>31</sup></code> should be clamped to <code>-2<sup>31</sup></code>, and integers greater than <code>2<sup>31</sup> - 1</code> should be clamped to <code>2<sup>31</sup> - 1</code>.</li>
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<li>Return the integer as the final result.</li>
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</ol>
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<p><strong>Note:</strong></p>
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<ul>
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<li>Only the space character <code>' '</code> is considered a whitespace character.</li>
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<li><strong>Do not ignore</strong> any characters other than the leading whitespace or the rest of the string after the digits.</li>
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</ul>
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<p> </p>
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<p><strong>Example 1:</strong></p>
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<pre>
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<strong>Input:</strong> s = "42"
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<strong>Output:</strong> 42
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<strong>Explanation:</strong> The underlined characters are what is read in, the caret is the current reader position.
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Step 1: "42" (no characters read because there is no leading whitespace)
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^
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Step 2: "42" (no characters read because there is neither a '-' nor '+')
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^
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Step 3: "<u>42</u>" ("42" is read in)
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^
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The parsed integer is 42.
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Since 42 is in the range [-2<sup>31</sup>, 2<sup>31</sup> - 1], the final result is 42.
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</pre>
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<p><strong>Example 2:</strong></p>
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<pre>
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<strong>Input:</strong> s = " -42"
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<strong>Output:</strong> -42
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<strong>Explanation:</strong>
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Step 1: "<u> </u>-42" (leading whitespace is read and ignored)
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^
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Step 2: " <u>-</u>42" ('-' is read, so the result should be negative)
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^
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Step 3: " -<u>42</u>" ("42" is read in)
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^
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The parsed integer is -42.
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Since -42 is in the range [-2<sup>31</sup>, 2<sup>31</sup> - 1], the final result is -42.
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</pre>
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<p><strong>Example 3:</strong></p>
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<pre>
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<strong>Input:</strong> s = "4193 with words"
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<strong>Output:</strong> 4193
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<strong>Explanation:</strong>
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Step 1: "4193 with words" (no characters read because there is no leading whitespace)
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^
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Step 2: "4193 with words" (no characters read because there is neither a '-' nor '+')
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^
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Step 3: "<u>4193</u> with words" ("4193" is read in; reading stops because the next character is a non-digit)
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^
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The parsed integer is 4193.
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Since 4193 is in the range [-2<sup>31</sup>, 2<sup>31</sup> - 1], the final result is 4193.
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</pre>
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<p> </p>
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<p><strong>Constraints:</strong></p>
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<ul>
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<li><code>0 <= s.length <= 200</code></li>
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<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>
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</ul>
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