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Easiest way to win. Make a 1 block hallway, about 3-4 blocks long with fake walls. Block off 1 side of the hallway, stand in the hallway so the zombies will come in 1 by 1. Take out pistol. Hold down spacebar. Achivement.
You can leave the computer as it is, all you need to do is hold down space, so press it down with something heavy and do something else in the meantime.
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