[Leetcode_08 string conversion integer (atoi)] - [difficulty: in]

table of Contents:

• topic
• Script and notes
• Script Logic

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topic:

Atoi you to implement a function, it can convert a string to an integer.

First, the function will begin with a space character discard useless if necessary, until the find to the first non-space character so far.

When we find the first non-space character is a positive or negative number, the combination of the symbols as much as possible with consecutive numbers up later, as the sign of integer; if the first non-space character is figures, which directly after the continuous numeric characters are combined to form an integer.

In addition to the string after a valid integer part may also exist extra characters, these characters can be ignored, they should not affect a function.

Note: if the character string in the first non-space character is not a valid integer character string is empty or contains only white space character string, then you will not need to be a function of conversion.

In any case, if the function can not effectively convert, 0 is returned.

Description:

We assume that the environment can store 32-bit signed integer size, then the numerical range [-231 231--1]. If the value exceeds this range, return INT_MAX (231 - 1) or INT_MIN (-231).

Example 1:

Input: "42"
Output: 42
Example 2:

Input: "-42"
Output: -42
Explanation: a first non-blank character '-', it is a negative sign.
  We will all digital consecutive negative number and later combined as much as possible, and finally get -42.
Example 3:

Input: "4193 with words"
Output: 4193
Explanation: converting the digital OFF '3', because the next character is not numeric.
Example 4:

Input: "words and 987"
Output: 0
Explanation: a first non-blank character 'w', but it is not a positive number or negative number.
Therefore, the conversion can not be performed effectively.
Example 5:

Input: "-91283472332"
Output: -2147483648
explanation: the number "-91283472332" Over the range of 32-bit signed integer.
  So return INT_MIN (-231).

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Script and notes: [time-consuming: 32ms]

class Solution:
    def myAtoi(self, str: str) -> int:
        str2 = str.strip()
        n1 = len (str2)
        tar1 = ""
        if n1 == 0:
            return(0)
        else:
            for i in range(n1):
                if str2[i].isdigit():
                    tar1 += str2[i]
                elif str2[i] == "+" or str2[i] == "-":
                    if tar1 == "":
                        tar1 += str2[i]
                    else:
                        break
                else:
                    break
        try:
            tar2 = int(tar1)
            if tar2 > 2 ** 31 - 1 or (-2)**31 > tar2:
                if 0 > tar2:
                    return((-2)**31)
                else:
                    return(2**31 -1)
            else:
                return(tar2)
        except ValueError:
            return(0)

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Script logic:

1. This title belongs to the conditions of screening questions: the number of cases, the selection criteria in line with the
In view of the understanding of the subject: traversal of a given character string added to the variable number, if encounter the following situation is stopped:
1. If the character is a word, then stop the walk, the storage variable to judge
2. If you encounter the "+" or "-" symbol is judged based on the variable storage case, if the memory variable is empty, then add the characters; otherwise stop the walk
3. ...
2. After traversing completed, another step is to judge and deal with overflow