LeetCode-Read N Characters Given Read4 II

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 may be called multiple times.

Solution:

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

public class Solution extends Reader4 {
    char[] tempBuf = new char[4];
    int offset = 4;
    int maxLen = 4;

    /**
     * @param buf
     *            Destination buffer
     * @param n
     *            Maximum number of characters to read
     * @return The number of characters read
     */
    public int read(char[] buf, int n) {
        int ind = 0;
        while (offset < maxLen && ind < n) {
            buf[ind++] = tempBuf[offset++];
        }
        if (maxLen < 4) return ind;
        
        ind = readFile(buf, ind, n);
        return ind;
    }

    public int readFile(char[] buf, int ind, int n) {
        int num = 4;
        while (num == 4 && ind < n) {
            num = read4(tempBuf);
            int end = Math.min(num, n - ind);
            for (offset = 0; offset < end; offset++) {
                buf[ind++] = tempBuf[offset];
            }
        }
        maxLen = num;
        return ind;
    }
}