158. Read N Characters Given Read4 II - Call multiple times.py

# The API: int read4(char *buf) reads 4 characters at a time from a file.

# The return value is the actual number of characters read. For example, it returns 3 if there is only 3 characters left in the file.

# By using the read4 API, implement the function int read(char *buf, int n) that reads n characters from the file.

# Note:
# The read function may be called multiple times.
# The read4 API is already defined for you.
# @param buf, a list of characters
# @return an integer
# def read4(buf):

class Solution(object):
	# save prev buffer
    def __init__(self):
        self.__buf4 = [''] * 4
        self.__i4 = 0
        self.__n4 = 0
        
    def read(self, buf, n):
        """
        :type buf: Destination buffer (List[str])
        :type n: Maximum number of characters to read (int)
        :rtype: The number of characters read (int)
        """
        i = 0
        while i < n:
            if self.__i4 < self.__n4:  # Any characters in buf4.
                buf[i] = self.__buf4[self.__i4]
                i += 1
                self.__i4 += 1
            else:
                self.__n4 = read4(self.__buf4)  # Read more characters.
                if self.__n4:
                    self.__i4 = 0
                else:  # Buffer has been empty.
                    break
        
        return i