Leetcode 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.
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)
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; } }
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