15. Read N Characters Given Read4 II - Call multiple times

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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 may be called multiple times.

解法1：

这题其实针对的是在I中的解法里的一个问题，就是多读的buf会被扔掉。
这里因为要call multiple times,那么不能扔掉多读的，而是要存起来。
存起来的办法就是建一个queue,先读queue里的数，如果有多的就放回到queue里。
C++

1

Java

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/* 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
     */
    Queue<Character> queue = new LinkedList<>();
    public int read(char[] buf, int n) {
        int i = 0;
        while (i < n && !queue.isEmpty()) {
            buf[i++] = queue.poll();
        }
        // i points to the next inserting position
        while (i < n) {
            char[] buffer = new char[4];
            int len = read4(buffer);
            if (len == 0) {
                return i;
            }
            int j = 0;
            for (; j < len && i < n; j++) {
                buf[i++] = buffer[j];
            }
            while (j < len) {
                queue.offer(buffer[j++]);
            }
        }
        return i;        
    }
}