157. Read N Characters Given Read4 π
Description
Given a file
and assume that you can only read the file using a given method read4
, implement a method to read n
characters.
Method read4:
The API read4
reads four consecutive characters from file
, then writes those characters into the buffer array buf4
.
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[] buf4 Returns: int buf4[] is a destination, not a source. The results from read4 will be copied to buf4[].
Below is a high-level example of how read4
works:
File file("abcde"); // File is "abcde", initially file pointer (fp) points to 'a' char[] buf4 = new char[4]; // Create buffer with enough space to store characters read4(buf4); // read4 returns 4. Now buf4 = "abcd", fp points to 'e' read4(buf4); // read4 returns 1. Now buf4 = "e", fp points to end of file read4(buf4); // read4 returns 0. Now buf4 = "", fp points to end of file
Method read:
By using the read4
method, implement the method read that reads n
characters from file
and store it in the buffer array buf
. Consider that you cannot manipulate file
directly.
The return value is the number of actual characters read.
Definition of read:
Parameters: char[] buf, int n Returns: int buf[] is a destination, not a source. You will need to write the results to buf[].
Note:
- Consider that you cannot manipulate the file directly. The file is only accessible for
read4
but not forread
. - The
read
function will only be called once for each test case. - You may assume the destination buffer array,
buf
, is guaranteed to have enough space for storingn
characters.
Example 1:
Input: file = "abc", n = 4 Output: 3 Explanation: After calling your read method, buf should contain "abc". We read a total of 3 characters from the file, so return 3. Note that "abc" is the file's content, not buf. buf is the destination buffer that you will have to write the results to.
Example 2:
Input: file = "abcde", n = 5 Output: 5 Explanation: After calling your read method, buf should contain "abcde". We read a total of 5 characters from the file, so return 5.
Example 3:
Input: file = "abcdABCD1234", n = 12 Output: 12 Explanation: After calling your read method, buf should contain "abcdABCD1234". We read a total of 12 characters from the file, so return 12.
Constraints:
1 <= file.length <= 500
file
consist of English letters and digits.1 <= n <= 1000
Solutions
Solution 1
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