uvalive4849的ac源码。算法：2-sat。题意：给n（n<=3000）个黑方块的坐标，保证黑方块没有公共边。对于每个黑方块选一个角作为结点，使得所选结点满足输入的一个无向图。其中距离为曼哈顿距离。输出是否有解。possible或impossible。-AC source of uvalive 4849. Algorithms: 2-sat. Meaning of the questions: to n (n <= 3000) coordinates a black box, to ensure that there is no common edge black squares. For each black box to choose a corner as nodes, such that the selected nodes meet a directed graph with no input. Where the distance is the Manhattan distance. Output is solvable. possible or impossible.