[LeetCode] 158. Read N Characters Given Read4 II - Call multiple times

原题连接：https://leetcode.com/problems/read-n-characters-given-read4-ii-call-multiple-times/

这道题是http://blog.youkuaiyun.com/foolnote/article/details/50621629的升级版，这里要求目标函数能够被多次调用。所以出现了一个情况，就是上次read4()读回来的字符还没完全被取完。我们要先去buffer里面取，取不到了后才再次调用read4()函数去读字符。

代码如下:

public class Solution extends Reader4 {
    /**
     * @param buf Destination buffer
     * @param n   Maximum number of characters to read
     * @return    The number of characters read
     */
    int index = 0;
    int count = 0;
    char[] buffer4 = new char[4];
    public int read(char[] buf, int n) {
        int actRead = 0;
        boolean isEnd = false;
        while(!isEnd && actRead<n)
        {
            if(count == 0)
            {
                count = read4(buffer4);
                if(count<4)
                    isEnd = true;
            }
            while(count>0 && actRead<n)
            {
                buf[actRead] = buffer4[index];
                actRead++;
                index++;
                count--;
                index = index%4;
            }
        }
        return actRead;
    }
}