string_to_integer.py

Class Solution(object):
  def atoi(self, str):
    str=str.strip()
    if not str:
      return 0
    
    MAX_INT=2147483647
    MIN_INT=-2147483648
    ret=0
    overflow=False
    pos=0
    sign=1
    
    if str[pos]='-':
      pos += 1
      sign = -1
    if str[pos]='+':
      pos += 1
    
    for i in range(pos, len(str)):
      if not str[i].isdigit:
        break
      ret=ret*10+int(str[i])
      if not MIN_INT<=sign*ret<=MAX_INT:
        overflow=True
        break
      
    if overflow:
      return MAX_INT if sign==1 else MIN_INT
    else:
      return sign*ret