157 Read N Characters Given Read4

题意不是很理解

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 theread4API, implement the functionint read(char *buf, int n)that readsncharacters from the file.

Example 1:

Input: 
buf =
"abc", n = 4

Output:
 "abc"

Explanation:
 The actual number of characters read is 3, which is "abc".

Example 2:

Input: 
buf = "abcde", n = 5 

Output: 
"abcde"

/* 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
     */
    //abcd efgh lmn 
    public int read(char[] buf, int n) {
        char[] temp = new char[4];
        int index = 0;
        //use temp to store what you read from read4
        //and then write it to buf
        while (true) {
            int count = read4(temp);//不停的读到TEMP。读到没内容或者到达N
            //我真正需要的，是MIN(COUNT, N - INDex)
            count = Math.min(count, n - index);
            for (int i = 0; i < count; i++) {
                buf[index++] = temp[i];
            }
            //two situation to end the loop
            //index == n read enough
            //content is not enough
            if (index == n || count <4) {
                return index;
            }
        }


    }
}