String to Integer (atoi)

The key idea

Problem

Implement the myAtoi(string s) function, which converts a string to a 32-bit signed integer.

The algorithm for myAtoi(string s) is as follows:

1. Whitespace: ignore any leading whitespace (' ').
2. Signedness: determine the sign by checking if the next character is '-' or '+', assuming positivity if neither is present.
3. Conversion: read the next characters until the next non-digit character or the end of the input is reached. The rest of the string is ignored.
4. Rounding: if the integer is out of the 32-bit signed integer range [-2^31, 2^31 - 1], then round the integer to remain in the range. Specifically, integers less than -2^31 should be rounded to -2^31, and integers greater than 2^31 - 1 should be rounded to 2^31 - 1.

Return the integer as the final result.

Constraints

• 0 <= s.length <= 200
• s consists of English letters (lower-case and upper-case), digits (0-9), ' ', '+', '-', and '.'

Examples

Complexity

Time: O(n) Space: O(1)

More String problems

• Find the Index of the First Occurrence in a StringEASY
• Length of Last WordEASY
• Longest Common PrefixEASY
• Repeated Substring PatternEASY
• Reverse String IIEASY
• Text JustificationHARD
• Verifying an Alien DictionaryEASY
• Zigzag ConversionMEDIUM