Read N Characters Given Read4
Created: November 19, 2018 by [lek-tin]
Last updated: October 3, 2019
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.
Example 1
Input: buf = "abc", n = 4
Output: "abc"
Explanation: The actual number of characters read is 3, which is "abc".
Example 2
Input: buf = "abcde", n = 5
Output: "abcde"
Note
The read function will only be called once for each test case.
Solution
"""
The read4 API is already defined for you.
@param buf, a list of characters
@return an integer
def read4(buf):
# 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'
buf = [' '] * 4 # Create buffer with enough space to store characters
read4(buf) # read4 returns 4. Now buf = ['a','b','c','d'], fp points to 'e'
read4(buf) # read4 returns 4. Now buf = ['e','f','g','h'], fp points to 'i'
read4(buf) # read4 returns 3. Now buf = ['i','j','k',...], fp points to end of file
"""
"""
The read4 API is already defined for you.
@param buf, a list of characters
@return an integer
def read4(buf):
# 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'
buf = [' '] * 4 # Create buffer with enough space to store characters
read4(buf) # read4 returns 4. Now buf = ['a','b','c','d'], fp points to 'e'
read4(buf) # read4 returns 4. Now buf = ['e','f','g','h'], fp points to 'i'
read4(buf) # 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)
"""
curr, size = 0, 4
while curr < n:
tempBuf = ["" for _ in range(size)]
# n can be longer than the file size
# take the min to decide whether to stop
# "abc", 3
# "abcdef", 5
chunk = min(read4(tempBuf), n-curr)
# If chunk == 0, file has been read completely
if chunk == 0:
break
print(chunk)
buf[curr: curr+chunk] = tempBuf
curr += chunk
return curr