[LeetCode] 157. Read N Characters Given Read4

 Problem : https://leetcode.com/problems/read-n-characters-given-read4/

Use intermediate buffer to read 4 bytes every time.

"""
The read4 API is already defined for you.

    @param buf4, a list of characters
    @return an integer
    def read4(buf4):

# Below is an example of how the read4 API can be called.
file = File("abcdefghijk") # File is "abcdefghijk", initially file pointer (fp) points to 'a'
buf4 = [' '] * 4 # Create buffer with enough space to store characters
read4(buf4) # read4 returns 4. Now buf = ['a','b','c','d'], fp points to 'e'
read4(buf4) # read4 returns 4. Now buf = ['e','f','g','h'], fp points to 'i'
read4(buf4) # read4 returns 3. Now buf = ['i','j','k',...], fp points to end of file
"""

class Solution:
    def read(self, buf, n):
        """
        :type buf: Destination buffer (List[str])
        :type n: Number of characters to read (int)
        :rtype: The number of actual characters read (int)
        """
        
        copied = 0
        read = 0
        buf4 = [''] * 4
        
        while copied < n:   
            read = read4(buf4)
            if read > 0:
                for i in range(min(read, n-copied)):
                    buf[copied] = buf4[i]
                    copied += 1
            else:
                break
        
        return copied