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.

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解题思路：

开始理解题意错误，每次读入4个字符，不是从buf里读入的，而是从文件里读入的，存入buf. 如果read4 < 4, 则说明已读到文件结尾。同时想到file.length > n, 则每次要确定读入Buf的正确长度，即Max.min(count, n - total)

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Java code:

/* 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) {        boolean eof = false; //end of file        char[] temp = new char[4];        int total = 0;        while(!eof && total < n){            int count = read4(temp);            if(count < 4){                eof = true;            }            // get the actual count            count = Math.min(count, n - total);            for(int i = 0; i< count; i++){                buf[total++] = temp[i];            }        }        return total;    }}

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Reference:

1. https://leetcode.com/discuss/44743/another-accepted-java-solution

2. http://bangbingsyb.blogspot.com/2014/11/leetcode-read-n-characters-given-read4.html