IO Buffer & H-Index

Read N Characters Given Read4

读一个文件最终有两个结果

1. 把文件读完了，但是没有读到n个字符，返回总过读了多少个字符。
2. 文件读完了或者没有读完，返回n。

/* 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) {
        int readBytes = 0;
        char[] temp = new char[4];
        boolean eof = false;

        while (!eof && readBytes < n) {
            int count = read4(temp);
            if (count < 4) {
                eof = true;
            }

            int length = Math.min(count, n - readBytes);
            for (int i = 0; i < length; i++) {
                buf[readBytes++] = temp[i];
            }
        }
        return readBytes;
    }
}

Read N Characters Given Read4 II - Call multiple times

比如我们有一个文件叫[a, b]。如果第一次我们调用read(buf, 1)，我们能在文件里读到[a]。但是如果我们坚持了上一题的做法，read4这个方法已经把整个文件都读完了，那我们再次调用read(buf, 1)，我们无法读到任何字符。因此在这题里，我们需要在全局里cache下上一次read4读出的，但是在上一次的结果里没有被用到的characters。

/* 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
     */

    int remaining = 0, offset = 0;
    boolean eof = false;
    char[] temp = new char[4];

    public int read(char[] buf, int n) {
        int readBytes = 0;
        while (readBytes < n && (!eof || remaining != 0)) {
            int readLength = 0;
            if (remaining != 0) {
                readLength = remaining;
                remaining = 0;
            } else {
                offset = 0;
                readLength = read4(temp);
                if (readLength < 4) {
                    eof = true;
                }
            }
            int length = Math.min(readLength, n - readBytes);
            for (int i = offset; i < offset + length; i++) {
                buf[readBytes++] = temp[i];
            }
            remaining = readLength - length;
            if (remaining != 0) {
                offset += length;
            }
        }
        return readBytes;
    }
}