2020/2/10leetcode06

class Solution:
def myAtoi(self,str:str)->int:
    numdic={"0":0,"1":1,"2":2,"3":3,"4":4,"5":5,"6":6,"7":7,"8":8,"9":9}
    i=0
    while i<len(str) and str[i]==" ":
        i+=1
    if i>len(str) or (str[i] not in numdic and str[i] not in ("+","-")):
        return 0
    sign=1
    if str[i]=="-":
        sign=-1
        i+=1
    elif str[i]=="+":
        i+=1
    num=0
    boundry=(1<<31)-1 if sign>0 else 1<<31
    while i< len(str) and str[i] in numdic:
        num=num*10+numdic[str[i]]
        i+=1
        if num>boundry:
        return sign*boundry
    return sign*num