LeetCode 157: 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 readsn characters from the file.

Note:
The read function will only be called once for each test case.

int read(char* buf, int n) {
  int len = 0;
  while(n > 0) { // if no length left, ends.
      int tmp = min(read4(buf), n);
      n = n - tmp;
      len = len + tmp;
      buf += tmp;  // buf need to be increased.
      if(tmp < 4) break;  // if tmp < 4, means ending.
  }
  return len;
}