Table of Contents

## Question

Implement the `myAtoi(string s)`

function, which converts a string to a 32-bit signed integer (similar to C/C++’s `atoi`

function).

The algorithm for `myAtoi(string s)`

is as follows:

- Read in and ignore any leading whitespace.
- Check if the next character (if not already at the end of the string) is
`'-'`

or`'+'`

. 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. - 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.
- Convert these digits into an integer (i.e.
`"123" -> 123`

,`"0032" -> 32`

). If no digits were read, then the integer is`0`

. Change the sign as necessary (from step 2). - If the integer is out of the 32-bit signed integer range
`[-2`

, then clamp the integer so that it remains in the range. Specifically, integers less than^{31}, 2^{31}- 1]`-2`

should be clamped to^{31}`-2`

, and integers greater than^{31}`2`

should be clamped to^{31}- 1`2`

.^{31}- 1 - Return the integer as the final result.

**Note:**

- Only the space character
`' '`

is considered a whitespace character. **Do not ignore**any characters other than the leading whitespace or the rest of the string after the digits.

**Example 1:**

Input:s = "42"Output:42Explanation:The underlined characters are what is read in, 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: "42" ("42" is read in) ^ The parsed integer is 42. Since 42 is in the range [-2^{31}, 2^{31}- 1], the final result is 42.

**Example 2:**

Input:s = " -42"Output:-42Explanation:Step 1: " -42" (leading whitespace is read and ignored) ^ Step 2: " -42" ('-' is read, so the result should be negative) ^ Step 3: " -42" ("42" is read in) ^ The parsed integer is -42. Since -42 is in the range [-2^{31}, 2^{31}- 1], the final result is -42.

**Example 3:**

Input:s = "4193 with words"Output:4193Explanation:Step 1: "4193 with words" (no characters read because there is no leading whitespace) ^ Step 2: "4193 with words" (no characters read because there is neither a '-' nor '+') ^ Step 3: "4193 with words" ("4193" is read in; reading stops because the next character is a non-digit) ^ The parsed integer is 4193. Since 4193 is in the range [-2^{31}, 2^{31}- 1], the final result is 4193.

**Constraints:**

`0 <= s.length <= 200`

`s`

consists of English letters (lower-case and upper-case), digits (`0-9`

),`' '`

,`'+'`

,`'-'`

, and`'.'`

.

## Python Solution

class Solution: def myAtoi(self, s: str) -> int: if len(s)==0: return 0 i=0 sign = 1 while s[i]==' ' and i<len(s)-1: i+=1 s = s[i:] l = len(s) if l==0: return 0 if s[0]=='+' or s[0]=='-': if l==1: return 0 elif s[1]=='+' or s[1]=='-': return 0 else: sign = [-1,1][s[0]=='+'] s = s[1:] l = l-1 temp = '0' for i in range(l): if s[i].isdigit(): temp += s[i] else: break intmax = 2**31-1 intmin = -2**31 if int(temp)*sign>=intmax: return intmax elif int(temp)*sign<=intmin: return intmin else: return int(temp)*sign