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 reads n characters from the file.

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

/* 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   Maximum number of characters to read
     * @return    The number of characters read
     */
    public int read(char[] buf, int n) {
        for(int i = 0; i < n; i += 4){
            char[] buffer = new char[4];
            int length = read4(buffer);//read4 每次读4个char
            System.arraycopy(buffer, 0, buf, i, length);
            if(length < 4){
                return  Math.min(i + length, n);//读到最后file里面char不足的时候 不是返回n
            }
        }
        return n;
    }
}