题目链接：http://poj.org/problem?id=1488
技巧：简单的字符串替换

 public static void main(String args[]) {    
        Scanner cin  = new Scanner(System.in);
        String line;
        boolean flag = false;
        while(cin.hasNext()){
            line = cin.nextLine();
            for (int i = 0; i < line.length(); i++) {
                if (line.charAt(i)=='\"') {
                    if (flag) {
                        line = line.replaceFirst("\"", "''");
                        flag = false;
                    } else {
                        line = line.replaceFirst("\"", "``");
                        flag = true;
                    }
                } 
            }
            
            System.out.println(line);
        }

    }