初めに
今回もLeetCodeをやっていきます。
今回の問題は以下
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:
Whitespace: Ignore any leading whitespace (" ").
Signedness: Determine the sign by checking if the next character is '-' or '+', assuming positivity if neither present.
Conversion: Read the integer by skipping leading zeros until a non-digit character is encountered or the end of the string is reached. If no digits were read, then the result is 0.
Rounding: If the integer is out of the 32-bit signed integer range [-231, 231 - 1], then round the integer to remain in the range. Specifically, integers less than -231 should be rounded to -231, and integers greater than 231 - 1 should be rounded to 231 - 1.
Return the integer as the final result.
Example 1:
Input: s = "42"
Output: 42
Explanation:
The underlined characters are what is read in and 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)
^
Example 2:
Input: s = " -042"
Output: -42
Explanation:
Step 1: " -042" (leading whitespace is read and ignored)
^
Step 2: " -042" ('-' is read, so the result should be negative)
^
Step 3: " -042" ("042" is read in, leading zeros ignored in the result)
^
Example 3:
Input: s = "1337c0d3"
Output: 1337
Explanation:
Step 1: "1337c0d3" (no characters read because there is no leading whitespace)
^
Step 2: "1337c0d3" (no characters read because there is neither a '-' nor '+')
^
Step 3: "1337c0d3" ("1337" is read in; reading stops because the next character is a non-digit)
^
Example 4:
Input: s = "0-1"
Output: 0
Explanation:
Step 1: "0-1" (no characters read because there is no leading whitespace)
^
Step 2: "0-1" (no characters read because there is neither a '-' nor '+')
^
Step 3: "0-1" ("0" is read in; reading stops because the next character is a non-digit)
^
Example 5:
Input: s = "words and 987"
Output: 0
Explanation:
Reading stops at the first non-digit character 'w'.
Constraints:
0 <= s.length <= 200
s consists of English letters (lower-case and upper-case), digits (0-9), ' ', '+', '-', and '.'.
回答
class Solution:
def myAtoi(self, s: str) -> int:
# 先頭の空白を除去
s = s.lstrip()
if not s:
return 0
sign = 1
idx = 0
# オプショナルな符号の処理
if s[0] in ('+', '-'):
# 符号の直後の文字が数字でなければ、変換失敗として 0 を返す
if len(s) == 1 or not s[1].isdigit():
return 0
if s[0] == '-':
sign = -1
idx += 1
result = ""
while idx < len(s) and s[idx].isdigit():
result += s[idx]
idx += 1
if result == "":
return 0
number = sign * int(result)
# オーバーフローのチェック（必要なら）
if number < -2**31:
return -2**31
if number > 2**31 - 1:
return 2**31 - 1
return number
最後に
普通に難しかったd