String to Integer (atoi) -- leetcode

天了嚕，條件真多

• 大體題意：

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. If the correct value is out of the range of representable values, INT_MAX (2147483647) or INT_MIN (-2147483648) is returned.

• 代碼如下：

class Solution:
    # @param {string} str
    # @return {integer}
    def myAtoi(self, str):
        FlagOfNegative = False
        MaxInteger = 2147483647
        MinInteger = -2147483648
        ret = 0
        if str == None or str == '':
            return 0
        while str[0] == ' ':
            str = str[1:]
        if str[0] == '-' :
            FlagOfNegative = not FlagOfNegative
            str = str[1:]
        elif str[0] == '+':
            str = str[1:]
        if str[0] > '9' or str[0] < '0':
            return 0
        for each in str:
            if each <='9' and each >= '0':
                ret = ret *10 + int(each)
            else:
                break
        if FlagOfNegative:
            ret = -1 * ret
        if ret > MaxInteger:
            return MaxInteger
        elif ret < MinInteger:
            return MinInteger
        return ret

def main():
    test = Solution()
    print test.myAtoi('   -1434aa32000')

if __name__ == '__main__':
    main()

• result：AC！！！
• 總結下：改了不下五次，各種限制條件，還是easy級別的。。真是的，不過沒什麼奇特的解題姿勢，就是都要考慮到就好了