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

Given a file and assume that you can only read the file using a given method  read4 , implement a method read to read n characters. Your method read may be called multiple times.

 

Method read4:

The API  read4 reads 4 consecutive characters from the file, then writes those characters into the buffer array buf .

The return value is the number of actual characters read.

Note that  read4() has its own file pointer, much like FILE *fp in C.

Definition of read4:

    Parameter:  char[] buf
    Returns:    int
Note: buf[] is destination not source, the results from read4 will be copied to buf[]

Below is a high level example of how read4 works:

File file("abcdefghijk"); // File is "abcdefghijk", initially file pointer (fp) points to 'a'
char[] buf = new char[4]; // Create buffer with enough space to store characters
read4(buf); // read4 returns 4. Now buf = "abcd", fp points to 'e'
read4(buf); // read4 returns 4. Now buf = "efgh", fp points to 'i'
read4(buf); // read4 returns 3. Now buf = "ijk", fp points to end of file

 

Method read:

By using the read4 method, implement the method  read that reads n characters from the file and store it in the buffer array  buf . Consider that you cannot manipulate the file directly.

The return value is the number of actual characters read.

Definition of read:

    Parameters:	char[] buf, int n
    Returns:	int
Note: buf[] is destination not source, you will need to write the results to buf[]

 

Example 1:

File file("abc");
Solution sol;
// Assume buf is allocated and guaranteed to have enough space for storing all characters from the file.
sol.read(buf, 1); // After calling your read method, buf should contain "a". We read a total of 1 character from the file, so return 1.
sol.read(buf, 2); // Now buf should contain "bc". We read a total of 2 characters from the file, so return 2.
sol.read(buf, 1); // We have reached the end of file, no more characters can be read. So return 0.

Example 2:

File file("abc");
Solution sol;
sol.read(buf, 4); // After calling your read method, buf should contain "abc". We read a total of 3 characters from the file, so return 3.
sol.read(buf, 1); // We have reached the end of file, no more characters can be read. So return 0.

 

Note:

1. Consider that you cannot manipulate the file directly, the file is only accesible for read4 but  not for read .
2. The read function may be called multiple times .
3. Please remember to RESET your class variables declared in Solution, as static/class variables are persisted across multiple test cases . Please see here for more details.
4. You may assume the destination buffer array,  buf , is guaranteed to have enough space for storing  n  characters.
5. It is guaranteed that in a given test case the same buffer buf is called by read .