Read N Characters Given Read4

Source

• leetcode: 157

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.

题解

题目意思是给你一个read4的函数，实现一个readn的函数。

一开始题目一直没搞懂，原来，read4(buf) 是指，读4个字符存到buf，或者读剩下的不足四个的字符，返回的数字是存到buf里的字符数。

java

/* 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;
    }
}