human: Given a node-centered hypergraph: <hypergraph>, where nodes represent papers and hyperedges represent sets of papers co-cited by a source paper.

Details of the hypergraph:
Center node: "tetris is hard even to approximate"
  Abstract: In the popular computer game of Tetris, the player is given a sequence of tetromino pieces and must pack them into a rectangular gameboard initially occupied by a given configuration of filled squares; any completely filled row of the gameboard is cleared and all pieces above it drop by one row. We prove that in the offline version of Tetris, it is NP-complete to maximize the number of cleared rows, maximize the number of tetrises (quadruples of rows simultaneously filled and cleared), minimize the maximum height of an occupied square, or maximize the number of pieces placed before the game ends. We furthermore show the extreme inapproximability of the first and last of these objectives to within a factor of p^(1-epsilon), when given a sequence of p pieces, and the inapproximability of the third objective to within a factor of (2 - epsilon), for any epsilon>0. Our results hold under several variations on the rules of Tetris, including different models of rotation, limitations on player agility, and restricted piece sets.

Connected through hyperedge HE-1 (induced by source paper "the computational complexity of angry birds"):
  with members:
    - "the computational complexity of portal and other 3d video games"
    - "pspace completeness of bloxorz and of games with 2 buttons"
    - "braid is undecidable"
    - "a bayesian ensemble regression framework on the angry birds game"
    - "bejeweled candy crush and other match three games are np hard"
    - "towards a theory of mind inspired generic decision making framework"
    - "candy crush is np hard"
    - "classic nintendo games are computationally hard"

Connected through hyperedge HE-2 (induced by source paper "the computational complexity of fire emblem series and similar tactical role playing games"):
  with members:
    - "computational complexity of games and puzzles"
    - "trainyard is np hard"
    - "on planar variants of the monotone satisfiability problem with bounded variable appearances"
    - "the computational complexity of portal and other 3d video games"
    - "candy crush is np hard"
    - "classic nintendo games are computationally hard"
    - "lemmings is pspace complete"
    - "the complexity of the puzzles of final fantasy xiii 2"

Connected through hyperedge HE-3 (induced by source paper "lasertank is np complete"):
  with members:
    - "gaming is a hard job but someone has to do it"

Connected through hyperedge HE-4 (induced by source paper "computational complexity of games and puzzles"):
  with members:
    - "the computational complexity of portal and other 3d video games"
    - "combinatorial game complexity an introduction with poset games"
    - "classic nintendo games are computationally hard"
    - "lemmings is pspace complete"
    - "gaming is a hard job but someone has to do it"
    - "spider solitaire is np complete"

Connected through hyperedge HE-5 (induced by source paper "hanabi is np hard even for cheaters who look at their cards"):
  with members:
    - "bejeweled candy crush and other match three games are np hard"
    - "candy crush is np hard"
    - "the computational complexity of the game of set and its theoretical applications"
    - "playing games with algorithms algorithmic combinatorial game theory"

Connected through hyperedge HE-6 (induced by source paper "on a generalization of eight blocks to madness"):
  with members:
    - "candy crush is np hard"
    - "classic nintendo games are computationally hard"
    - "there is no 16 clue sudoku solving the sudoku minimum number of clues problem"

Connected through hyperedge HE-7 (induced by source paper "bejeweled candy crush and other match three games are np hard"):
  with members:
    - "candy crush is np hard"
    - "gaming is a hard job but someone has to do it"

Connected through hyperedge HE-8 (induced by source paper "candy crush is np hard"):
  with members:
    - "where are the hard manipulation problems"
    - "tetravex is np complete"

Question: Please tell me which class the center node belongs to. The 40 classes are: cs.NA(Numerical Analysis), cs.MM(Multimedia), cs.LO(Logic in Computer Science), cs.CY(Computers and Society), cs.CR(Cryptography and Security), cs.DC(Distributed, Parallel, and Cluster Computing), cs.HC(Human-Computer Interaction), cs.CE(Computational Engineering, Finance, and Science), cs.NI(Networking and Internet Architecture), cs.CC(Computational Complexity), cs.AI(Artificial Intelligence), cs.MA(Multiagent Systems), cs.GL(General Literature), cs.NE(Neural and Evolutionary Computing), cs.SC(Symbolic Computation), cs.AR(Hardware Architecture), cs.CV(Computer Vision and Pattern Recognition), cs.GR(Graphics), cs.ET(Emerging Technologies), cs.SY(Systems and Control), cs.CG(Computational Geometry), cs.OH(Other Computer Science), cs.PL(Programming Languages), cs.SE(Software Engineering), cs.LG(Machine Learning), cs.SD(Sound), cs.SI(Social and Information Networks), cs.RO(Robotics), cs.IT(Information Theory), cs.PF(Performance), cs.CL(Computation and Language), cs.IR(Information Retrieval), cs.MS(Mathematical Software), cs.FL(Formal Languages and Automata Theory), cs.DS(Data Structures and Algorithms), cs.OS(Operating Systems), cs.GT(Computer Science and Game Theory), cs.DB(Databases), cs.DL(Digital Libraries), cs.DM(Discrete Mathematics). Directly output the class name.

gpt: cs.CC(Computational Complexity)