[LeetCode] String to Int

문제

Implement atoi which converts a string to an integer.

The function first discards as many whitespace characters as necessary until the first non-whitespace character is found. Then, starting from this character, takes an optional initial plus or minus sign followed by as many numerical digits as possible, and interprets them as a numerical value.

The string can contain additional characters after those that form the integral number, which are ignored and have no effect on the behavior of this function.

If the first sequence of non-whitespace characters in str is not a valid integral number, or if no such sequence exists because either str is empty or it contains only whitespace characters, no conversion is performed.

If no valid conversion could be performed, a zero value is returned.

Note:

• Only the space character ' ' is considered as whitespace character.
• Assume we are dealing with an environment which could only store integers within the 32-bit signed integer range: [−231,  231 − 1]. If the numerical value is out of the range of representable values, INT_MAX (231 − 1) or INT_MIN (−231) is returned.

Example 1:

Input: "42" Output: 42

Example 2:

Input: " -42" Output: -42 Explanation: The first non-whitespace character is '-', which is the minus sign.   Then take as many numerical digits as possible, which gets 42.

Example 3:

Input: "4193 with words" Output: 4193 Explanation: Conversion stops at digit '3' as the next character is not a numerical digit.

Example 4:

Input: "words and 987" Output: 0 Explanation: The first non-whitespace character is 'w', which is not a numerical   digit or a +/- sign. Therefore no valid conversion could be performed.

Example 5:

Input: "-91283472332" Output: -2147483648 Explanation: The number "-91283472332" is out of the range of a 32-bit signed integer.   Thefore INT_MIN (−231) is returned.

 

Approach

예외 처리와의 싸움

1. 앞에 +나 -가 오는 것 처리

2. 000000...으로 시작하는거 처리. 그러면서도 0인건 찾아내야함

3. 숫자가 Int범위를 넘어가는지 처리

솔직히 이런 문제는 한번에 맞추기 넘 어렵다

그리고 처음에는 일일이 '0'~'9', '-', '+' int값 알아내서 했었는데

isdigit()이라는 좋은게 있었다.

 

Code

https://github.com/chi3236/algorithm/blob/master/LeetCode_StringToInteger.cpp

chi3236/algorithm