read4() 每次读取的元素是 4 个。如果 n 可以被 4 整除，那么正好读完；如果不能被 4 整除，那么就需要在 n 的时候截止。
/* 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) {
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;
}
}
}
}
