B'The only difference between easy and hard versions are constraints on n and k . You are messaging in one of the popular social networks via your smartphone. Your smartphone can show at most k most recent conversations with your friends. Initially, the screen is empty (i.e. the number of displayed conversations equals 0 ). Each conversation is between you and some of your friends. There is at most one conversation with any of your friends. So each conversation is uniquely defined by your friend. You (suddenly!) have the ability to see the future. You know that during the day you will receive n messages, the i -th message will be received from the friend with ID id_i ( 1 <= id_i <= 10^9 ). If you receive a message from id_i in the conversation which is currently displayed on the smartphone then nothing happens: the conversations of the screen do not change and do not change their order, you read the message and continue waiting for new messages. Otherwise (i.e. if there is no conversation with id_i on the screen): Your task is to find the list of conversations (in the order they are displayed on the screen) after processing all n messages. The first line of the input contains two integers n and k ( 1 <= n, k <= 2 cdot 10^5) -- the number of messages and the number of conversations your smartphone can show. The second line of the input contains n integers id_1, id_2, ... , id_n ( 1 <= id_i <= 10^9 ), where id_i is the ID of the friend which sends you the i -th message. In the first line of the output print one integer m ( 1 <= m <= min(n, k) ) -- the number of conversations shown after receiving all n messages. In the second line print m integers ids_1, ids_2, ... , ids_m , where ids_i should be equal to the ID of the friend corresponding to the conversation displayed on the position i after receiving all'...