Read N Characters Given Read4

Total Accepted: 11222 Total Submissions: 37944 Difficulty: Easy 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.

思路

• 主要是特别难理解题意
• 其实read4(buf[]) 这个method的功能,就是自己去stream读取四个字符,然后保存到buf[] 这个char array数组里
• 理解了半天
• System.arraycopy这个函数的五个参数:source array, start index, target array, start index, number of element need to copy

public class Solution extends Reader4 {
    public int read(char[] buf, int n) {
        for(int i = 0; i < n; i += 4){
            char[] tmp = new char[4];
            // 将数据读入临时数组
            int len = read4(tmp);
            // 将临时数组拷贝至buf数组，这里拷贝的长度是本次读到的个数和剩余所需个数中较小的
            System.arraycopy(tmp, 0, buf, i, Math.min(len, n - i));
            // 如果读不满4个，说明已经读完了，返回总所需长度和目前已经读到的长度的较小的
            if(len < 4) return Math.min(i + len, n);
        }
        // 如果循环内没有返回，说明读取的字符是4的倍数
        return n;
    }
}