Read N Characters Given Read4

题目：

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 will only be called once for each test case.

 

解答：

public class Solution extends Reader4 {

    public int read(char[] buf, int n) {
        char[] buffer = new char[4];
        int readBytes = 0;
        boolean eof = false;

        while(!eof && readBytes < n) {
            int sz = read4(buffer);
            if(sz < 4) {
                eof = true;
            }

            int bytes = Math.min(n-readBytes, sz);
            // buffer:src
            // buf:dst
            // readBytes:destPos
            // bytes:length
            System.arraycopy(buffer, buf, readBytes, bytes);
            readBytes = readBytes + bytes;
        }

        return readBytes;
    }
}