[LeetCode][Algorithms]String to Integer (atoi)

# -*- coding: utf8 -*-‘‘‘__author__ = ‘[email protected]‘https://oj.leetcode.com/problems/string-to-integer-atoi/

Implement atoi to convert a string to an integer.

Hint: Carefully consider all possible input cases. If you want a challenge, please do not see below and ask yourselfwhat are the possible input cases.

Notes: It is intended for this problem to be specified vaguely (ie, no given input specs).You are responsible to gather all the input requirements up front.

Requirements for atoi:The function first discards as many whitespace characters as necessary until the first non-whitespace characteris found. Then, starting from this character, takes an optional initial plus or minus sign followed by as manynumerical 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 andhave 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 sequenceexists 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. If the correct value is out of the range ofrepresentable values, INT_MAX (2147483647) or INT_MIN (-2147483648) is returned.

===Comments by Dabay===主要就是处理各种情况：先把两边的引号和空格去掉。然后确定符号。接着读数字。最后判断越界。‘‘‘class Solution:    # @return an integer    def atoi(self, str):        str_new = str.strip("‘").strip(‘"‘).strip()        if str_new == "":            return 0

        result = 0        positive = True        start_flag = False        for i in xrange(len(str_new)):            if start_flag is False:                if str_new[i] == "-":                    positive = False                    start_flag = True                    continue                if str_new[i] == "+":                    start_flag = True                    continue            if str_new[i] in "0123456789":                start_flag = True                result = result * 10 + int(str_new[i])            else:                break

        if not positive:            result = result * -1        if result > 2147483647:            result = 2147483647        if result < -2147483648:            result = -2147483648

        return result

def main():    s = Solution()    print s.atoi(" -00012a3 +2")

if __name__ == "__main__":    import time    start = time.clock()    main()    print "%s sec" % (time.clock() - start)