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.
一刷
题解：与157不同的是，函数可以被多次调用，比如read(buf, 1), 但是我们访问read4，如果函数没有结束，一定读得了4个char，但是只返回一个。
buffPtr: buffer pointer
buffCnt: buffer counter, 保存一次调用read4读到的字符数目
直到buffPtr reach buffCnt的时候，置为0，准备调用下一次read4
/* 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
*/
private int buffPtr = 0;//buffPointer
private int buffCnt = 0;//buffCounter
private char[] buff = new char[4];
public int read(char[] buf, int n) {
int ptr = 0;
while(ptr<n){
if(buffPtr == 0){
buffCnt = read4(buff);
}
if(buffCnt == 0) break;
while(ptr<n && buffPtr < buffCnt){//if buffPtr reach the buffCnt, set to zero and ready
buf[ptr] = buff[buffPtr];
ptr++;
buffPtr++;
}
if(buffPtr>=buffCnt) buffPtr = 0;
}
return ptr;
}
}
