Read N Characters Given Read4

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.

注意：It assumes only read less than n chars, even if the there are more than n chars in a file.

public int read(char[] buf, int n) {
  boolean eof = false;      // end of file flag
  int total = 0;            // total bytes have read
  char[] tmp = new char[4]; // temp buffer
  
  while (!eof && total < n) {
    int count = read4(tmp);
    
    // check if it's the end of the file
    eof = count < 4;
    
    // get the actual count
    count = Math.min(count, n - total);
    
    // copy from temp buffer to buf
    for (int i = 0; i < count; i++) 
      buf[total++] = tmp[i];
  }
  
  return total;
}

reference：https://discuss.leetcode.com/category/166/read-n-characters-given-read4