Read N Characters Given Read4

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 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

思路：就是每次read4只能读一次，然后根据count决定是否加入buf，注意考虑读出来的是0，则直接break，不读了。

/**
 * The read4 API is defined in the parent class Reader4.
 *     int read4(char[] buf);
 */

public class Solution extends Reader4 {
    /**
     * @param buf Destination buffer
     * @param n   Number of characters to read
     * @return    The number of actual characters read
     */
    public int read(char[] buf, int n) {
        char[] buf4 = new char[4];
        int count = 0;
        
        while(true) {
            int size = read4(buf4);
            for(int i = 0; i < size && count < n; i++) {
                buf[count++] = buf4[i];
            }
            if(size == 0 || count == n) {
                return count;
            }
        }
    }
}