8000 8. String to Integer (atoi) · nullskill/leetcode@e3dd267 · GitHub
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8. String to Integer (atoi)
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‎lib/src/medium/8.string_to_integer_atoi/main.dart

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class Solution {
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int myAtoi(String s) {
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s = s.trim();
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if (s.isEmpty) return 0;
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bool isNegative = false;
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if (s[0] == '-') {
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isNegative = true;
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s = s.substring(1);
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} else if (s[0] == '+') {
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s = s.substring(1);
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}
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String digits = '0123456789';
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int result = 0;
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for (var i = 0; i < s.length; i++) {
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if (!digits.contains(s[i])) break;
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result = result * 10 + int.parse(s[i]);
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if (isNegative && -result < -2147483648) {
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return -2147483648;
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} else if (!isNegative && result > 2147483647) {
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return 2147483647;
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}
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}
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return result *= isNegative ? -1 : 1;
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}
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}
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void main(List<String> args) {
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print(Solution().myAtoi('-2147483648'));
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print(Solution().myAtoi('9223372036854775808'));
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print(Solution().myAtoi('words and 987'));
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print(Solution().myAtoi('42'));
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print(Solution().myAtoi('+-12'));
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print(Solution().myAtoi(' -42'));
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print(Solution().myAtoi('+4193 with words'));
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}

‎lib/src/medium/8.string_to_integer_atoi/problem.txt

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8. String to Integer (atoi)
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https://leetcode.com/problems/string-to-integer-atoi/
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Implement the myAtoi(string s) function, which converts a string
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to a 32-bit signed integer (similar to C/C++'s atoi function).
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The algorithm for myAtoi(string s) is as follows:
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Read in and ignore any leading whitespace.
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Check if the next character (if not already at the end of the string) is '-' or '+'.
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Read this character in if it is either. This determines if the final result is negative
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or positive respectively. Assume the result is positive if neither is present.
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Read in next the characters until the next non-digit character or the end of the input
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is reached. The rest of the string is ignored.
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Convert these digits into an integer (i.e. "123" -> 123, "0032" -> 32).
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If no digits were read, then the integer is 0. Change the sign as necessary (from step 2).
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If the integer is out of the 32-bit signed integer range [-231, 231 - 1],
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then clamp the integer so that it remains in the range. Specifically, integers less than -231
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should be clamped to -231, and integers greater than 231 - 1 should be clamped to 231 - 1.
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Return the integer as the final result.
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Note:
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Only the space character ' ' is considered a whitespace character.
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Do not ignore any characters other than the leading whitespace or the rest of the string after the digits.
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Example 1:
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Input: s = "42"
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Output: 42
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Explanation: 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: "42" ("42" i EDBE s 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 [-231, 231 - 1], the final result is 42.
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Example 2:
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Input: s = " -42"
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Output: -42
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Explanation:
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Step 1: " -42" (leading whitespace is read and ignored)
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^
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Step 2: " -42" ('-' is read, so the result should be negative)
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^
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Step 3: " -42" ("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 [-231, 231 - 1], the final result is -42.
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Example 3:
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Input: s = "4193 with words"
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Output: 4193
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Explanation:
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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: "4193 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 [-231, 231 - 1], the final result is 4193.
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Constraints:
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0 <= s.length <= 200
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s consists of English letters (lower-case and upper-case), digits (0-9), ' ', '+', '-', and '.'.

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