# String to Integer (atoi) – LeetCode Solutions

LeetCode has a Medium coding Problem in Its’ Algorithm Section in Python “String to Integer (atoi)”. Today We are going to solve this problem. LeetCode Link of the Problem is HERE.

#### 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:

1. Read in and ignore any leading whitespace.
2. 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.
3. Continue reading the characters until you reach the next non-digit character or the end of the input. Ignore rest of the string.
4. 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).
5. If the integer is out of the 32-bit signed integer range `[-231, 231 - 1]`, then clamp the integer so that it remains in the range. Specifically, integers less than `-231` should be clamped to `-231`, and integers greater than `231 - 1` should be clamped to `231 - 1`.
6. 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.

Examples

Input: s = “42” Output: 42

Explanation: 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 [-231, 231 – 1], the final result is 42.

Input: s = ” -42″ Output: -42

Explanation: 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 [-231, 231 – 1], the final result is -42.

Input: s = “4193 with words” Output: 4193

Explanation: 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 [-231, 231 – 1], the final result is 4193.

Conditions

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

#### Solution to String to Integer (atoi)

The Skeleton Code given in LeetCode is

class Solution(object):

def myAtoi(self, s):

“”” :type s: str

:rtype: int

“”””

Firstly, I Created Four variables r, Sign, and Number_start. r is used as a return variable where only numbers are taken out of the input string. The Sign variable is declared to check that which sign is present in the input sentence. The Number_start variable checks whether the numbers are started in the String or not. The fourth variable is a list of numbers 0 to 9.

Secondly, I initiated a loop starting from the start of the string to the end of the string.

Thirdly, Check in the String if the Character appears is present in the numbers variable then concatenate that to the r string.

In addition, Check for the Character, if it is +, – or space deal with it accordingly.

Moreover, Check for the appearance of characters apart from numbers, if any other character is present in the middle of numbers then break the loop.

Finally, Check for the sign, and Whether the returned integer is 32 bit or not, and do code accordingly.

Final Solution

class Solution(object):
def myAtoi(self, s):
“””
:type s: str
:rtype: int
“””
r = “”
sign = “”
Number_Start = False
numbers = [‘0′,’1′,’2′,’3′,’4′,’5′,’6′,’7′,’8′,’9’]
for i in s:
if i in numbers:
Number_Start = True
r+= i
elif i == “-“:
if Number_Start:
break
else:
Number_Start = True
if sign == “”:
sign = “-“
else:
return 0
elif i == “+”:
if Number_Start:
break
else:
Number_Start = True
if sign == “”:
sign = “+”
else:
return 0
elif i == ” “:
if Number_Start:
break
pass
else:
break
if r == “”:
return 0
if sign == “-“:
sign += r
if int(sign) <= -2147483648:
return -2147483648
return int(sign)
if int(r) >= 2147483648:
return 2147483647
return int(r)

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