49.把字符串转换为整数

题目描述

将一个字符串转换成一个整数，要求不能使用字符串转换整数的库函数。 数值为0或者字符串不是一个合法的数值则返回0

输入描述:

输入一个字符串,包括数字字母符号,可以为空

输出描述:

如果是合法的数值表达则返回该数字，否则返回0

# -*- coding:utf-8 -*-
class Solution:
    def StrToInt(self, s):
        # write code here
        if s=='':return 0
        nums = ['0','1','2','3','4','5','6','7','8','9']
        labels = ['+','-']
        sign = 1
        if s[0] in labels:
            if s[0]=='-':
                sign = -1
            s = s[1:]
        final_num = 0
        for char in s:
            if char not in nums:
                return 0
            else:
                final_num = final_num*10 + nums.index(char)
        final_num = sign*final_num
        if final_num<=0x7FFFFFFF and final_num>=(-0x7FFFFFFF-1):
            return final_num
        else:
            return 0